I'm tending to agree with the OP.
I don't see the argument against it for overpoweredness as being valid, since as many people have already said, you, 3 heroes and 0-4 henchies is pretty strong already if you know what you're doing. Maybe not for every class, but you and 7 henchies could get most done if you're patient and willing to learn. And really, they don't seem to care if you're overpowered in PvE, especially if you have 7/8 of the drops absorbed by AI. They're already changing heroes and henchies in PvP, which is where the balance issues really come into play.
In order to make a better-than-hench team of yourself and 7 heroes, you'd have to have invested a lot of time playing: learning, unlocking, gathering equipment, etc. So why not let us control a full team if we want to put in that kind of time? The henchies are still there if you need a profession you can't build better yourself.
Besides the primary missions and quests that require a certain hero or two, having tricked out heroes with fabulous tuned-for-AI builds is not a starting requirement of the game - it's a
possible goal in the game.
Lots of people have already proved that heroes are unnecessary in Tyria and Cantha by henching all or most of it. I haven't tried, but I suspect you could hench most of Elona without your choice of 3 heroes, too. A player's heroes tend to be about as strong as the player himself. I've seen players with hero builds that are just downright frightening and make even Alesia look like SuperMonk! I've seen those same players get into wipes or near-wipes and blame it on the henchies.
Maybe if you let those players try building a whole team themselves, they'd finally start to realize that there are easier, stronger ways to approach PvE.
The people that like PUGing will still like it, and they'll still do it. The people that don't like PUGing now take heroes? Well, we used to just take henchies.

I keep an eye on the local chat in towns. If I see someone requesting help in a way that makes me think it's someone I won't wind up being sorry to have helped, I'll still join with them if I can (you find some very nice new guildies that way.) Cruddy henchies, better henchies, 0 heroes, 3 heroes or 7 heroes ... I've always played that way.