The real problem isn't that people are playing what they're having fun with, it's the fact the "trinity" warrior/rogue/mage is forced on you.
Let me illustrate what the real problem is...
- Is it perfectly viable to clear a map with 4 of the same class? -> Yes, in fact it's quite powerful
- Is is possible to open every treasure rooms with 4 of the same class? -> No, for every class missing you get at least 3 doors for that class
Bioware did something very wrong, they force down our throats an unnecessary trinity because of their definition of "fun". Since they couldn't make the game only completable with the trinity, they punish us another way (gold/item). We have to follow them like sheeps or we pay the price, it's a horrible design. What Bioware should do is to remove that non-sense and be sure to only have doors openable by the classes in the party. You have 2 warriors and 2 rogues? You only see warrior and rogue doors, no mage door. You have 4 mages, you only see mages doors. It's not like it's impossible to do...
I actually disagree completely.
Anyone who has ever played either old-fashioned RPGs or MMOs (And I know DA:I is just a single player RPG with a tacked on multiplayer aspect, but the SINGLE PLAYER of the series has always enforced this point!) knows that any good party has multiple roles: A wall to soak up damage, supporters to keep that wall alive, damging units that excel in killing single powrful threats, AOE attackers, etc....
Basically, what I'm getting at is, try playing WoW with a party of only Rogues. Or only Warriors. Doesn't freaking work. Sure, you might be able to do decently early on, but try a mid-game instance, and your ass is pulverized.
DAI is certainly more lenient, but the roles exist; notice how the game starts you off with one tank, one ranged damager, and one supportive mage. Clearly this was done intentionally in order to encourage familiarity with team tactics early on,
Basically, the genre of RPGs in general, not even just online ones, is largely divided into roles. And if you want to play a specific role, find a party that role works well in. I have the common courtesy to change my played character to another role, if I can. As such, I ask that others have the common courtesy to not go "LOL 3/1 OR 2/2, WHO NEEDS A THIRD CLASS!?" Even if all the gear you find behind the doors/ buy with the gold sucks, you can still salvage them for materials!