It's all in your head.
I used 16:9 since release 2012 until 2019 cause it looked better. Couldn't play 4:3 cause game just looked trash. Changed to 1440x1080 and I can just see better at distance and through the edges of smokes. If you don't have any boomer issues as I do, play whatever you want. You prefer bigger FOV? 16:9, otherwise 4:3.
Playing better, worse... all in your head. Only change I do is the colour of my crosshair. If I play shit I change the colour. It reminds myself that I need to get my shit together.
Sometimes you also play a lot and play like trash and sometimes you have 20hrs/2 weeks and play like a god. I was afk, came back and was dogshit. Now I have 20hrs/2 weeks and last two days I was fucking insane. No warmup, just come home from work, instaQ and rekt everyone. I am sure end of week I will be garbage again, but it will just my mind playing tricks.
Other times I pracc, warmup, have 60hrs and play like shit. It's just in your mind. Stay chill, focus on the game. You will have good games again. If you feel too many emotions, stop playing. Go dm with music. Try again tomorrow with chill attitude. You will have good game again.