Good question. I’m trying to recall. I want to say yes, you start gaining weight faster as time progresses (don’t quote me on that however lol). Last career mode i made it to the top in was during early access. Fights did get harder, just can’t remember the exact reason at the moment.
I’m in a career now, so we’ll find out for sure soon I suppose. This career mode is very precise, I will say that. Every single stat, while seeming like it might not mean something, has small effects. Your overall rating will drop by as much as 3 - 5 points if you’re out of weight standards before a fight and you can feel a decline in sharpness as well. Those are things I’ve direct for sure noticed recently.
Lastly, I suggest to stay away from Pro and Undisputed difficulty. Those levels blatantly cheat.