Ok, this was kinda interesting thread (before all this easy/hard, bot/human flame started). I'll do my best to ignore the flame.
While quite interesting, 1st post is quite controversial. I'll try to break it into parts and answer them separately (some of this stuff was mentioned before but I want to voice my opinion as well)
1. "
veteran Guild Wars players are better suited to evolving and adapting" hypothesis.
I'm not sure if I fit this category, but I fit the description given by the OP. I played for more than 2 years but I don't feel like I'm all mighty and awesome at the game. I know the ropes but for the most part I just Crit Barrage my way through the game with 3 Necro heroes and henchies tagging along. It works like a charm and I hardly need to adapt. If I fail horribly I'll probably bring a different build to counter this situation. But truth to be told, it's not necessary in most situations. Crit Barrage is enchantment dependent build but I breeze through enchantment stripping with ease. I just target call and henchies drop the enemies for me. If I feel like my team needs me I just target call those with enchantment stripping powers 1st and use my full power after they're dead.
Actually as far as I can remember I changed my builds and tried to adapt way more when I was new to the game. Now that I have my trusty highly customizable heroes I just roll through everything with the well-rounded team and don't bother for maximum efficiency. If someone fails the team will still be victorious. I recall getting through the Hells Precipice mission with 2 fire ele heroes on my team without too much trouble. I felt like mobs didn't seem to die fast enough but I didn't bother to think about it twice. It was a final mission after all =)
2. "
players would be further entertained by an additional power to gain after max level" hypothesis.
I'm not sure about this one. GW was positioned as "less grind involved, it's skill that matters" title. In fact we have this stuff in the form of title dependent PvE skills. And I don't like this pressure of "you gotta max those titles to get the best out of your skills" stuff. I consider fun I get from playing to be my reward and that's enough =)
3. "
GW players will start playing other MMO games" hypothesis.
For me that's no true. If a game has monthly payment requirement, it's not for me. If it has micro-payments and privileged accounts it's not for me as well. I don't want extensive amounts of grind to get to the top. I want instant map travel and ability to respec freely. GW is still pretty unique.
4. "
ex-GW players will for communities in other MMO games" hypothesis.
I'm not sure about this one. I've played quite a few MMOGs before I started playing GW and I never saw this happening. I saw guilds moving to the next games but I never saw communities based on "previous game" filter. On the other hand I have no proof of this being uncommon so I won't comment on this one =)
Bottom line: ex-GW players dominating other games is not likely IMO