not true, having your Thumb in a 45° angle on the D-Pad is the optimal way to play a fighting game. in that position you can easily roll and press any direction without moving your thumb an inch
this is also how most people held the SNES controller for example:
notice how the shape of the controller and the positioning of the D-Pad almost automatically make you use the D-Pad at a 45° angle, and that's a controller that many still call the best 2D controller ever.
which one looks more comfortable to do fast rolls with in a fighting game?
the one where all 4 sides are covered and all you have to do is literally tilt your thumb around?
or the one where you don't cover everything quite as well and you have to move your thumb around?
I know I vastly prefer the first one for sure. and whenever I play a fighting game on a PS4 or PS5 controller, I never hold my controller firmly like I do when playing other games, I always hold it a bit like this:
(just imagine the thumb being on the D-Pad here... that's the closest I found online lol)
my left hand will be tilted away from the handle to get a good coverage on the d-pad
on an analog stick on the other hand, you want your thumb to be more straight on, because it's way easier to precisely move in cardinal directions if your thumb is oriented in a north/south position.
of course you will get used to it in any position after a while but still