Let me break it down for you:
If the clutch is depressed you wont damage anything at all, no matter what gearbox is used and what gear you're in.
IRL you cant just shift down with a H-pattern gearbox, you need to use the clutch to not break the transmission, but you cant keep it completely depressed, because then you wont get any help from the engine braking, and therefore you'll get understeer and that is what you experience in-game @
Gr8888T . The car has no engine brake, therefore it doesn't stop as well and doesn't turn as well. the answer to this problem IRL is heel and toe technique. In-game you dont need to worry about breaking the gearbox so its no problem, simply dont use the clutch. you can actually steer the car with the engine brake, downshifting earlier turns the car more into the corner, and waiting with the downshift causes more understeer but makes the car more stable.
With a sequential gearbox you don't need to use the clutch IRL either, just lift of the throttle when shifting, up or down.
And there is no difference if you use the stick shifter or the paddles, no matter if its a G27 or a DFGT its the completley same signals you send to the game.
And doing heel-toe on the streets might be fun, I do it aswell, but its completely unnecessary, you never drive that fast on the streets anyway, and if you do, you're an idiot.
@
Macapaca : what do you mean you dont want to risk your gearbox? drive like a normal human being and it will never be a problem! heel-toe will, if not done exactley right, wear out your clutch eventually.