Many people with working legs choose to drive. It doesn't mean they don't go to the gym. Actually people even drive to the gym! (surprise, I know)
Many people drive to the gym to play on their phones, sure. But the kind of person who drives generally won't do much actual working out.
You’re describing an extreme so let me counter with a different “what if” extreme: If
, every day, you use a wheel chair for five minutes and run for several hours followed by 200 squats then your legs will not atrophy. My point is that writing papers is only one way to work your mind and using llm’s for this does not indicate how you use your mind overall.
Regardless of the existence of other ways to exercise your legs which you also will not do, because you're a person with working legs who chooses to use a wheelchair.