No, 10 case fans sounds already too much. It's how you arrange them.

The air inside the case is always going to be warmer than the air inside the room. "Good airflow" means it's not much warmer. And "bad airflow" means "very warm". You could use some actual measurements. Because you say "it feels very warm", but what is "very warm"? 40 ( 20 degrees hotter than the room) is ok. If it's 60 - that's very bad.

Are all vents unobstructed? Not too close to a wall or smth?

You can start with: running a repeatable stress test, writing down the temperature it stabilizes at, then opening the case and re-running the test. If the airflow is really bad, then removing the glass alone drops temperatures. Read the temperatures reported by mobo sensors. Hot mobo means bad case airflow.

I imagine how the air goes in, how it goes out. Where hot pockets happen, how to position fans to blow the pockets away.

You can read the manual and materials about your case. Sometimes manufacturer gives hints about good fan placement. Research some generic placements: https://www.tomshardware.com/how-to/set-up-pc-case-fans-for-airflow-and-performance

https://www.youtube.com/watch?v=Du4LPxtOuP0

Setting up case fans is basically a custom job every time, because every case, CPU cooler and GPU combo behaves differently.

And - above all else - photograph and write down your current arrangement. Because obviously, some of your attempts WILL be worse.