Theres nothing broken about a class that revolves around defense, just as Monk revolves around support, even he has been granted a powerful offensive support capability, and likewise, a class which stresses defense will have at least one offensive attribute, if not 2. It only takes one or 2 attributes and a new group of skills to provide those defensive capabilities, and making the blind assumption that that is all it will do because the entire idea is not detailed here is ignorant.
There is no miscommunication with Crom, he has a very small perspective and missunderstands.
As for mass teleportation, that is a form of mobility. Teleportation is the ultimate speed of mobility, and being able to mass teleport is truely overpowered and broken IMO. And also disfunctional. The only thing I percieve mass teleporting is all of your Ritualist spirits to a new location, teleporting around your allies is unwelcome. As always, any skill that takes control of your ally, or even your enemy in such extreme cases, is unwelcome in this game, this is a one unit control game, and your one unit is all your controling.
Now making gates isn't as bad, but being able to bridge all of your units any significant amount of distance is an extreme, let me repeat EXTREME capability. There are group mobility skills in Warrior and Paragon attributes, with Charge, and more than one Paragon skill, you can increase the movement of an entire party, teleporting an entire party is just broken. Likewise, there are paragon and elementist skills which allow you to increase the speed of select members, granting them a movement bonus is fine. But even at a 1 minute recast, 25 energy, exhaustion, 10 second cast time, Elite, and every other cost in the game, bridging an entire party across any significant distance is overpowered. There are certain maps with teleporters which make different parts of the area closer, but being able to make your own is overpowered. The only way this could be balanced is if your portals were available to anyone, even ememies, in which case all your really doing is creating new paths for anyone to travel quickly, but even then, under the control of a player, it is still to powerful. It can be done, I can think of some great ways to do it, but too powerful, way.
As for Stealth, it already belongs on Assassin. If any class ever needed to get into or out of battle unseen to avoid damage, it is Assassin, and placing it on another class would never serve justice to Assassin. Beyond that, Stealth is a very unstable addition to a game, it can be done in many ways, but all of them have imbalance situations, or arn't effective enough to merit use. If you make someone totaly untargetable and unseen, than it is way overpowered, most skills which simply make you untargetable are Elites themselves, and if your only unseen, but can be targeted, than your really not hidden well enough to make a major impact, it will only count as a temporary surprise. Teleports already add the element of surprise, they allow you to close distance on an enemy quickly enough to throw the enemy for a loop, and expecially when they do not know which allie you are advancing on, it is hard to prepare for their assault when you don't have time to boost a particular allie as he closes on them. Sadly, most of these advancing teleports are even frequent enough to make normal use out of, so this advantage is another one hit wonder. If stealth is added to the game, Assassin should get just as many stealth skills as whatever other class gets them, IMO, the only way to make invisibility useful is if you turned invisible the moment you teleported to an enemy, leaving no visible trace of your location and forcing the enemy to search around for a target.
As I said before, the functions of every class can be broken down into offensive damage, defensive techniques, offensive support, defensive support and mobility. Everything falls into those catagories. For offensive damage there are attacks, spells, degen. Defense covers evasion, blocking, regen and healing. Offensive support includes interrupts, sabatoge, stripping, weakening, and attack boosting. Defensive support includes damage reduction, evasion, removal, healing and regen on teammates. Mobility includes running and teleporting either to or from enemies, or at all.
AI manipulation isn't a legitimate skill function because it should never be applied to an enemy, you use skills to cause incentives or disinsentives to enemies on their attacks, spells, or possition, but actually forcing them to make a move isn't accpetable. And skills which only apply to AI are not universal to other characters, so they arn't acceptable skills. AI manipulation, or even player maniplulation should never go beyond strategy, tactics and suppression.
Now if Stealth was added to the game, it would basicly count as a new function, but it would be so minor that it wouldn't make a significant impact. Just because enemies are invisible doesn't mean you cannot attack them, and if you cannot attack them, than that is an extremely broken defensive advantage, that is all there is too a stealth idea. Forms of steath which involve reducing agro circles of NPCs do not apply to players, and is part of AI manipulation, something that isn't functional.
The catagory of every function may fall within certain types, but that doesn't make them the same, different cost, different activation triggers, different application, different possitioning, different limitations. There are a vasad of factors which can be altered to make new skills which provide simular or same effects, in very different ways.
For instance, using attacks or spells which deal damage in a straight line, it is just another form of damage, but it works differently. It deals damage on more than one foe, but it doesn't deal damage to a loose group, it does damage in a line. Likewise, the defense and preperation against such an attack is different, if your avoiding line attacks than you dont stand in a freaking line, you spread out and stay seperate simular to group attack spells, but you can fight strafe eachother as long as the enemy isn't attacking from the side with a line attack, thus the gameplay changes for that kind of attack.
There is an old saying, "there is more than one way to skin a cat". You may assume that because the cat is skinned that it produces the same result, but that is just a lack of perspective, the cat could have been skinned alive, greusomely, it could have been bleed to keep the fur in good condition, it could have been done in strips to produce different lengths of fur, it could have been done as a whole to make one large piece, it could have been done quickly just to remove the fur so you can reach the meat, and I'm sure there are more ways if you really think about it (if you want to). Different ways produce different results, there is a difference if you recognize it.
It is no different than paragons defensive skills compared to Monks, most of monk skills provide evasion and damage reduction by an amount, paragons defense skills stress more damage reduction by a percent and armor. Monks skills are more singular for keeping one allie alive, Paragons skills are more plural, to keep a group alive. Both are dealing with the defensive support role, both in different ways, both influencing gameplay in different ways.
The more you distinguish each class, the more differences you will find, and the more distinguished the skills are, the more opportunities you will recognize between those functions, or in slight alterations and applications, and counters to a new kind of skill. The more accurate your observations are, the more original ideas you will come up with, it is as simple as that. Anyone who cannot come up with new functions and concepts, or imagines that every function is just a repeat of another simply lacks the perspective to distinguish the very legitimate and significant differences each capability has to offer.