Lol "tank rush"
if you mean light vehicle rush then you'll have to deal with raketenwerfer and panzershrecks which is fine. Earliest tanks come out way later, plenty of time for a jagdP4. There is no tank rush that is unbearable unless you are missing your fuel as well all game
Plus no one told you to go for the mech truck first, Med truck is also a great choice
Getting a t34 within 10 minutes is compeltely possible.
It's impossible to deploy the mechanized regiment, then battlegroup headquaters and then a jagdpanzer 4 within 10 minutes.
I'm usually against nerfing units of any faction, unless a stale meta is formed around it, like it was during the isu vs elefant times or during shocks vs flame.
By nerfing the puma you'd decrease the use of the mechanized regiment, since most people build to have reliable at in early to mid game. Stuka is usually produced when you encounter a blobber or somebody who entrenches with maxim spam.
I usually go for battlegroup headquaters, I just don't like that you want to take tactics and thereby versility away from the game.
I'd rather see a cost increase than a nerf, if it's inevitable.
This unit is designed to be a tank hunter, I have the feeling this people complain about a unit doing it's job. Likewise you could complain that a HMG supresses units and denies area.