XCOM is fairly unique in modern long-form games in that you shouldn't expect to win your first game. Most games have a mentality of making the game where you can't lose the game as a whole, just the individual missions. This is not one of those games. You're going to lose a few games before you win. Most of the things that seem like bullshit that comes out of nowhere can actually be planned against with careful tactics which you learn over the course of a few games.
This is the whole point of Ironman mode. XCOM on Ironman mode is a game that you can lose, and which you can't trial-and-error your way through. It's like playing Chess and complaining that you can't take back your move after the other player captures your piece.
Because no one ever gets mad at video games, right? Tell me more, master of cool
I had soldiers missing on 99% hit chance and enemies shooting snipers from across the map with aimbot-like accuracy.
A high probability of a hit still means there's a chance of a miss. If you play recklessly to get a high-percentage hit, there's still a chance you'll miss and pay for, say running out of cover right next to your target
That's not to say anything of the spontaneously combusting automobiles
They aren't. When a car is hit, it will catch fire. If your guy is in cover behind it, he'll say something like "this thing is going to blow". This means the car will explode on the next turn. You can also use this to your advantage (say two enemies are hiding behind a car, you can throw a grenade to deal 3 damage to each enemy and cause the car to explode the next turn, dealing extra damage and [if they're still alive] destroying their cover)
and lack of cover in certain chokepoints.
Then avoid those chokepoints. Dash past them or hold back and draw the enemies closer.