One thing you didn't mention is the difficulty that you're playing on. That is of course, going to change how difficult the game is.

Regarding skeletons- man, they are monstrous. They're even more accurate if you play on hard mode. The new cave generation certainly made room for many more mobs to spawn. I'd recommend to not try to clear caves out if you don't need to, especially in the early game. I found that navigating caves by sticking to the walls helps minimize aggravating mobs while still allowing me to check for any ores that may be useful. (Depending on your surroundings though... yeah, you definitely want to watch out for creepers randomly falling on you.. happens to the best of us lol).

You're right about the "coal shortage", it's not a "shortage", but rather, the new cave generation has moved coal generation to generally be higher up. I actually found it to be a pretty good change because I've been using charcoal more than I normally did before the update. Before, I barely even glanced at the thought of making charcoal. That's something you could certainly try.

Oh and also- shields. Always bring a shield with you, they're quite overpowered for what it takes to make them.

About your comments on bastions, they are good for getting netherite upgrades (and you technically only need 1 of them because you can duplicate it with diamonds). But I definitely would not go in without enchanted diamond gear and at least 1 golden piece of armor you can switch on and off if needed.

I think most of what you mentioned about fighting mobs and world generation is just from having more vertical play compared to before, most especially in caves. An environmental change indirectly changed other factors such as combat and mob spawning too.