In relation to the opening of speed tiers, did you see the recent warstory "Whack-a-mole"? ScarfChomp's speed became an issue against a scarfed Kojondo, iirc. I honestly think there hasn't been much speed climb (though obviously there's some every generation). Rather, I think the issue is that the speed tiers have diversified, with many non-standard speeds. Yes, 102 speed is still excellent, as it outspeeds many crtical threats, old and new (Salamence, Sazandora, Randorosu, Zapdos, Hihidaruma, etc). However, I think that the speed tiers have been becoming less strict ever since early D/P, and these numerous base speed stats that are not divisible by 5 are a large cause of it.
So, I guess the main conclusion that can be drawn from my point is that while Garchomp's speed is very nice, it's not so much amazingly trolly as it is just really handy for the uses that Garchomp has, which appear to be revenge killing against offense, or stall breaking against defense.