What is the advantage lyra? Thats a good question. One that we should have summed up early on in the discussion.
Thankfully we did. Feel free to check back but if not ill give a quick recap here.
Now while im not going to dig through and quote it all I will again list the main points (There are more but these are the main reasons to me).
No waiting time to form a team.
For a casual player who only has maybe 30-45 mins to play spending 10 on getting a team is a huge chunk of playtime gone. With 7 heroes people can spend more time playing the game and less time waiting to play.
You can go afk when you need to.
With players you cant expect people to wait for you while you go afk multiple times during the same mission. With 7 heroes they will be there when you get back.
Those are the 2 main points for me.
Now the obvious question from there would be why do you need 7 heroes when you have h/h?
Why? Because h/h is, to put it simply, not great.
Its extremely underpowered when compared to a team of 8 players. Outside of GW:EN the henchies have shocking builds, they dont even have 8 skills! Even in GW:EN most builds are fairly poor.
This means someone that is unable to pug is playing with a huge disadvantage.
Adding 7 heroes means people playing with heroes will be on a much closer playingfield to that of a team of 8 players. While it will never be as good, its a feature that is already partially ingame and would allow the casual player to play without being punished with weaker teams because they cant pug.
Now another big point although less than the previous two in my opinion.
Allowing casual players access to more of the game.
Im going to take HM as my example here, but it applies to the elite areas as well (Although some due to their nature cant be completed with 1 player, still a lot more of the game is opened up).
HM with the awful hench builds really isnt worth thinking about. So that leaves you with getting a team of players. Instantly a problem for the first 2 reasons. Lets assume however you have time and you know you wont get interrupted.
So to get a team for HM. Well in most areas there arent even enough people to get a team, let alone enough people doing HM to get a team, let alone enough people doing HM who happen to include the required proffesions.
So that doesnt work, lets try our guild/alliance. Ah your a casual player so you arent in a hardcore HM guild, sure you could leave and join one...but is being forced to join specific guilds just to play half the game really the way to do things?
Ok so lets try arranging a team on a forum. Well your a casual player so you cant arrange to be on at a set time, as a casual player you might not even know any GW forums! Also should players have to arrange to play the game? Why cant they just play it?
Ok now lets imagine we have 7 heroes. You log on, add your heroes, play.
If you need to log off or go afk your not ruining the game for anyone else, you can come back and play when it suits you.
Surely you can see how much that would help people out?
(As you can see my whole reasoning behind this is how it helps the casual player out, others have different opinions on why they think 7 heroes would be good for the game but im not going into them because...well they arent my opinions

. But it does go to show it doesnt just help 1 group of players, it helps a lot)