Maths isn't my background, but isn't this a serious flaw with the quality of the pseudo-random numbers it generates? I remember learning about the enigma machi

Maths isn't my background, but isn't this a serious flaw with the quality of the pseudo-random numbers it generates? I remember learning about the enigma machine and how it had a flaw where a letter could not be transformed into itself. And knowing that, for example, an A could never be a A was critical to cracking the enigma code. Because of that knowledge, my cryptographic intuition is that any seemingly minor fact like this could actually be a critical flaw.