I will first say, that the main draw for DnD is hanging out with friends and roleplaying, not so much the combat system. Now with a video game, that can be played single player and has very limited means for roleplay, it makes sense to want to dress up the combat portion of DnD to make it more exciting for a wider audience.
1. I agree with. I think it can be adjusted though. Like have backstab require stealth or flanking. Height giving advantage is simple and works with the current UI where you see your sum of advantages and disadvantages. Isn't good for balance though and I rather see height work like cover. Have it scale +1 to +5 AC and DEX saving throws depending on the height difference and add some range extension in as well.
2. I think you've misworded things? I'll assume you're talking about everyone having rogue's cunning action essentially. In which case, I do agree that should back. Shove, hide, disengage should be regular actions for non-rogues.
3. This is the big one. Now I like surfaces as they add more complexity to the game. It's really easy, in fact too easy to rest and regain your spell slots so you don't have to be conservative with spells versus cantrips. Now if they fix issue #1 and make spells that require a saving throw easier to hit, that will bring things back into balance. For context, enemies have a lowered AC that makes physical attacks and some spells easier to hit with. Larian went with lower AC and higher HP so people would miss less and be less frustrated, which I understand. They just need to tweak things and I think they can get there. I'd be one the people happy with that as it would make the gameplay more about strategy and less about luck by a degree.