Blood Mages, Disc, and Psion were very well designed, but all three were very much broken. DKs were poorly designed AND broken at the same time. Paladin and Cleric bled into each other way too much, although the Castigator stance was pretty awesome.
Druids were not unique, it was the same shit we had from every Druid class ever. Same for Necros.
Shamans were also fucking broken. I could cast an immediate LoH on a tanky bear pet for almost no mana on a 30? second timer. I was soloing 6 dot bosses at level 45-50. That's not good design, that's broken gameplay. Much like a DK running around in circles, grabbing 60 mobs, and spamming an aoe lifetap.
I think you're conflating the two ideas. Did they have some good ideas? Absolutely. I loved the class trees, like the three ways to play a Shaman, or the four affinities available for Clerics. But a lot of that shit needed to be worked out still. I mean Psions were literally unbeatable in PvP if they mezzed you once.
Why are you trying to downplay the classes when they were clearly awesome? You say 3 are very well designed but what about all the others? No game has ever done a Bard even half as good as Vanguard did. It had all the abilities you could ever want, lots of varied and interesting offensive attacks, defensive stuff, and control stuff, but it also had powerful songs and the player would create the songs bit by bit using song structures pieced together in a really clever and fun way. The Rogue was as good as in any game with all the usual stealthy stuff and attack abilities, but it also was an aggro managing class, reducing its own aggro but could also increase the aggro of the tank to help them grab targets. It was like a whole separate mini game built into an already good dps class. The Warrior was as good as in any game ever, RPG or MMO. The shammy could be split in 3 ways and each was drastically different, the bear shaman was as good a tank as anything, it couldn't hold aggro, but it could tank all day with heals. The bird shaman was really good dps, etc. Also the DK wasn't designed badly at all, it was a great class and super fun to play. It could teleport behind mobs, dot, tank, and do everything EQ SK could but much more and it and the pally were both just as good as the warrior in group content so they went a long way to killing the trinity.
Also the Druids might have been mostly the same as EQ, but the EQ druid was awesome as well, and in Vanguard they added the whole Phenomena points system on top which made it even more interesting. The Necro was the same, it took the EQ Necro which was one of the best classes in that game, and added the ability to graft different gear onto the pet using body parts of mobs you killed.
Whether they ended up OP or not doesn't really matter. That is about tuning and the game lacked that and a lot more, also a lot of the OP'ness came from the dumb gear SOE added to the game later on. But the actual design of the classes was awesome. Also they were a lot more balanced at release, things only got more out of whack later on when SOE added stupid stuff to the game because they didn't care. They added OP gear in quest lines when they added teleporting Rifts all over the place and more, to try to dumb it down for modern dude bro dumbasses, but they didn't even understand how it would affect some classes, and the DK was one of those classes. Originally you couldn't exploit lifetap at all because it just wasn't powerful enough with normal dropped and quested gear. You could tank 3 or 4 mobs and maybe survive because more mobs gave bigger lifetaps, but you also took more damage so tanking 3+ was dangerous. Most just sticked to 1 like the other classes. With some effort spent on balance all the classes would have been better than any game in every way.
Also the actual character building was better than any other game. You got a bunch of points to spend at multiple times in each level, like mini landmarks, and how you spent those points drastically changed the class. I built my bard as a tank originally and his dps was weak but he could take a real beating. I then respecced and his dps became about the best in the game, but he died in no time. Each class could be tweaked like that and it really let the player free to build their character how they wanted it to be. Most games are too scared of giving players the freedom to do that.
Everyone likes to dumb everything down into games either being awesome or shit, but usually it is never like that and Vanguard especially was a mixed bag. Some of the classes were miles ahead of any game, some needed more, but all were above average. Performance and bugs were terrible though, at release the game was barely even playable. I also didn't like dungeon design at all and found a lot of locations to be bland, and I would have preferred more quality over quantity when it came to questing. They should have had fewer but better ones, and made the player grind mobs like EQ sometimes. There was a lot more I didn't like too like how aggro worked, and how empty lots of areas was. I disliked as much as I liked, but the good stuff was really good.
p.s. All the classes I didn't mention are awesome too. Sorc: Reflecting spells back to the mob, tactically choosing when to make its own spells mana free or to crit, dots, snares, roots, aoes, dds, cone shaped, a mez, dispell, really good group buffs, etc..etc..