There's plenty of ways to incentivize the higher difficulty tuning other than just gear bloat. They could just keep the gear identical and only add appearances, or titles, tabards, mounts, etc.
It's ABSOLUTELY true. If you bring a Frost mage to 7.0 mythic, you're going to get grief, and to be honest, you probably should. Yes, you probably shouldn't, but most guilds aren't driven by mutual respect and a sense of comradery, they're driven by desire for loot.The problem is in part the idea that you need to bring a class that outperforms the median. That's not true at all. You need to bring players that can outperform the minimum on the classes they're playing. Of course, the further your group outperforms the minimum, the easier and faster time they'll have clearing the content.
That's a reach, imo. Class stacking was a result of players seeking the shortest path to getting what they wanted, pure and simple. If having 5 shamans to stack bloodlust was going to make dropping the loot easier, they'd do it. Whether there was multiple difficulty tiers was really irrelevant to that decision.The raiding min-max idea that is still causing these class stacking and viability issues was literally birthed in and fed by the single difficulty content system of Vanilla and BC (as well as previous MMOs).
No reason it can't be both. If Shadow priest damage without S2M is poor, then it's a pretty rational decision (in a utilitarian sense) to force raiders to take the spec. Why should 24 other players be expected to carry a sub-part spec in highly challenging content?Now, specifically regarding GungHo's issue, I'm not sure if it's an issue with WoW overall or if it's an issue with the group he tried to run with.
On the assumption that he's plenty geared and knows what he's doing, if he's trying to roll with a Mythic Group and Spriest is so far below average that most raids are excluding that spec from their raids, the issue is with Blizzard's balancing.
If he's trying to roll with a Normal or possibly Heroic group (and has appropriate gear and knows what he's doing) (or if the output potential of Spriest is still well above the minimum requirements for Mythic), then the person who excluded him from the raid is probably just a jerk.