1. Mega Evolutions are powerful stat wise, but most miss the lack of Life Orb when it comes to nuking everything. This gives them an advantage of bulk.
2. The introduction of faries hurt offense, not helped it. Now it's far less easy to drop around Outrage and Draco Meteor everywhere. Dragons and Fighting types were actually the most dangerous of offensive pokemon.
3. The weather nerf also helped stall more then it hurt it. Now we don't have base 180 Hydro Pumps and Fire Blast running around everywhere.
4. Stall isn't the only form of defense. Bulky Offense(which is more defensive) and Semi-Stall were not hurt nearly as much by Defog.
1. While the sheer power of the Megas does not necessarily increases compared to top LO threats, the same does not apply to their stall breaking ability, things like Megapinsir and Mixed Megachomp are simply painful to stall against(and unlikely to get ban). On the other hand, the fact that Mega does not switch in with increased defensive stats, and that they inherently misses leftover means that Megas are offensive in nature.
2. On paper faries are the best defensive typing along side steel, in realistic most faries are simply fragile on the physical side, and aims more at surviving a blow and fight back more than actually stalling out the game. And, to begin with, dragon type was not really that much a problem for defensive teams with so many steels running around.
3. I agree with you at this point
4. I don't see how bulky offensive can be more defensive
4.1 Defog does not necessarily hurt stalling that much, and switch focus stalling really appreciates its better distribution. It does hurt spikes a lot, but partially cancelled out by having more viable spikers (Chesnaught, Klefki), and was not something being relied so heavily to begin with.
However, there are something that you miss out.
1. The nerf to steel is simply terrible, I don't really think I need a second word about it
2. The buff to Knock off simply hurts. Not having leftover turns out to be crippling to certain defensive mon (e.g. Heatran). And we have yet to consider that it is an almost 100 BP nuke which gets through steel.
3. While we have increasing number of threats to be walled each generation, we still have only 6 teamslots, which means that the introduction of every new generation tends to favour offensive side inherently. This may be some how neutralised with some minor changes. Yet overall this generation is actually quite disappointing for stall players, as we do not really have much new toys to play with. Consider how we at least have Ferrothorn in last gen.