I'll agree to Grenade overuse in only one gamemode, which is Multi-team. Of course it will happen there, because there are usually very CQC maps being played. If you play Multi-team, prepare to die by grenades at least 4 or 5 times in the match.
Other than that instance, no. It's just a natural instinct it seems, that if someone has grenades, and you are in the room behind the corner, than they will chuck grenades at the threshold. But I think a lot of people would do the same if someone jumped into the room. Just lay a grenade down for your entrance, and say goodbye to your shields.
Armor Lock has always been one of the most hated things to bless Halo, I'll offer no argument there.
Power Weapons, it's all about the struggle to reach them. They've always been there like that. (besides Halo 4) Race them to it, and beat them to a pulp for even attemting to take your weapons. That's the mindset I use. If they do get their paws on them, then just be aware of that player. Try to give his power weapon a disadvantage by having leverage, or acting irrational in your movements. Once again, Multi-team does have blue team spawn next to the rocket on ascension. I don't know of any other instance however.