Your solution actually benefits bursty classes

It does literally the opposite. You're still looking at the trash as if that's where the bulk of the time is going to be spent, but if a fire mage for example blows their load into a boss taking 50% reduced damage, and can only manage ~2k base dps by the time the damage increase has ramped up, they're going to be useless. Fire mages/boomies are front loaded dps, especially for ST. The boss aspects of these changes specifically work against specs like them.

Lastly, a shifting meta is just as bad as a stale meta

That just doesn't make sense. Just basic math, having 6 "meta" dps specs instead of 3 is twice as good. Ya, you might only get invited every other week as an affliction lock, but that's a lot better than literally never getting invited, never getting a weekly chest, falling so far behind in gear they're screwed for the entire patch.

Is having to share the meta going to make fire mages sad? Ya. But it's going to make all the more ST oriented specs actually viable at least sometimes.