: It could happen in the original game but seemed accidental. In later games it
: seemed to be a designed behaviour.

I'm familiar with it in H1 of course, and when playing seriously I avoid trying to splatter Grunts for that reason, even though it wouldn't happen often. Mind you, I think maybe there is enough to time to jump out and get clear, if you do it immediately. But also it's definitely possible to just stay seated and survive (example in my movie BCM76 starting 4:27; also one in BCM134 starting 0:58).

Can't speak for the other games though. You say wheel arch, but I'm wondering how you know that. Have you checked footage often in Theater mode or something? In the first H1 example I mentioned, the grenade appears to be stuck to the underside.

: I suppose it's a game mechanism to make it clear that a revival is happening
: but it breaks immersion. It's hard to pretend that there is a real world
: thing going on.

Well, I'm sure 343 must have some explanation for what the light is. (Tried a brief search, gave up.)

: As I understand it, you can no longer just use the menu system to immediately
: revert to the last checkpoint.

That would surprise me a lot, if you mean the option no longer exists. Or do you just mean it's not available while you're downed?

: I haven't been a fan of significant named AI companions. They either wont die
: and just get in the way or they have to be cared for.

I rather doubt that I'd be interested in caring for them. With Reach I was always keen to know ways of taking AI buddies out of the picture, so I could be in full control of the combat (and also not have to listen to their repetitive dialogue). Same for Arby in H3.