>>43323374You clearly didn't play Gen VI OU or build a team during that time.
Outside of rare cases where there's a meaningful speed drop, like with Garchomp, a Mega is 100% better than all other possible sets.
What matters at that point is opportunity cost and managing the sole Mega on your team.
If you look at that thread, regular Latios is A rank while Mega Latios is untiered. Mega Latios is more powerful than Latios, but the stat boost mostly went to Attack, making it worse than Mega Latias (bulk, SpA), Mega Charizard X (Atk). With no change in speed tier, there's no reason to use Mega Latios over Latios + item as using it as your Mega hurts the overall team.
Mega Tyranitar is a perfect Mega with not a single point of wasted BST. The physical defense buff in particular is amazing. But there's a high opportunity cost using your stone on Tyranitar when it can still vomit rocks and pursuit well without it.