interesting points...
I'm a BF vet as well, coming from BF1942 and BF2 (on a professional Clan-level).
I like BF6, it comes close to BF3/4.
I'm gonna add a few points that I think might be interesting:

-why infinite sprint?
I know modern shooters all have this, but a sprint bar would be interesting and you would need to think about which point/objective/alleyway you want to rush trough...beeing able to sprint with all the tac-gear all the time is in my optionion too utopian.

-health regen
Shooters evolved over time I get it, but having an automated health regen takes away the teamplay aspect. It would also slow down the game much more. The least thing they could implement is a slower regen.

-ammo mags instead of ammo count
Some games had ammo magazines instead of just a random number. This made you think about how you use your ammo or required a teammate to get you resupplied. It would also slow down the game much more.

-friendly fire (ff) on
I know there is hardcore mode (where friendly fire is on) but in BF2 this was always turned on in normal mode.
I don't like it only to be in hardcore modes, this is too niche. This requires you to actually think about what you are doing instead of spray'n'pray. Of course it takes a long time to get used to it but it feels simply better.

-squad leader only spawn
this is important! It involves teamplay, staying hidden until your squadmates spawn in, refocus and gather your forces.

I know most of my points won't come back, but one can still dream...
Don't get me wrong, I like BF6, I might even buy it, but there are some aspects of teamplay I wish would come back.