The problem is not only that it's immersion breaking. It looks visualy stupid but it also completely break all the combats. A tactical game in which everything is an easy mechanic is not tactical anymore... Backstab is completely broken atm and even the heavier warrior in the heavier armor can backstab everyone in 1vs1.
What you describe "in Real life" absolutely don't looks like how backstab work in D&D, and it also look absolutely not accurate to reality... Exept if you can move way faster than your opponent... Which is something our characters aren't able to do in BG3 and D&D.