What's happening is some planes don't have flight models finished; they don't have realistic flight patterns/ "feels". For example, I just had a match against a few F2A bots while inside a tier 8 japan fighter. No matter how hard I tried, if I started the fight at equal speeds, 9/10 they could climb or match my speed in a level flight at 100 altitude, 1k, and 1.5k. I was gaining maybe 0.01 per 7 seconds, not moving and straight line flight at 1k altitude. That makes NO sense.
I ended up just alt f4ing the game because it was becoming such a joke. I then asked in general and it was confirmed they haven't finished that planes model yet. They are selling content for the game, monthly premium accounts, etc while the game itself is in open beta. Quite a few planes in the game don't even have remotely correct stats/hitboxes.
Classy!
Edit: I'm also finding this patch added a huge amount of bugs, such as when repairing a plane at a runway sometimes the plane will be DRASTICALLY slower after repair. I had a tier 7 fighter, lost a wing, repaired and could never get above 380 km/h without losing it in a level flight. Maybe just a weird bug, but I've noticed tons of other little quirks.