Yes, this is actually one thing in Sonic that's in such direct conflict with itself, it really doesn't have anything in the way of a "canon" resolution to it

It's silly to think that Sonic and co are complete "glass cannons" in the absence of rings... I think the better way to look at it is that even Eggman's most basic bots are actually quite lethal creations which can easily assassinate Sonic on their own, if he's not careful about hanging on to a ring.

It also speaks to the power of the rings that even a single one can make pretty much anybody, pretty much indestructible.

My only answer for it is... Sonic's body, right down to his biology, is durable to great speed. So perhaps those listed disasters he could survive by the "skin of his teeth". I don't know if "falling-speed" of atmospheric re-entry is faster than the speed of sound, but his body is ready for it.

But then again, it confuses me how Sonic can survive from great heights (he face-planted twice in Sonic Adventure and once in Unleashed) but can't survive bottomless pits.

Answer: It's a cartoon game series. They make up stuff as they go. You think in 1991 when they explicitly made Sonic the speed of sound they ever imagined he'd go at lightspeed, become a werewolf and face plant into earth 17 years later?

Technically, Sonic the Werehog was a hedgehog/Dark Gaia Creature hybrid, but I agree that Sonic Team isn't consistent with the tone or quality of the Sonic the Hedgehog series.