I’m trying to wrap my head around the idea of proficiencies and the act of acquiring more. When the characters are created they are based upon intelligence. When a character levels, new proficiencies are gained by save throw progression…thus penalizing which would normally be thought of as the more intelligent classes.
Only class proficiency acquisition varies by saving throw category, while general profs continue to accrue at a uniform rate across classes (granted, wizardy types tend to also level more slowly than others, so in practice they do gain general profs more slowly than other classes).
It’s a coincidence that wizards tend to have both a high intelligence and a low rate of proficiency acquisition.
The elven spellsword, for example, acquires class proficiencies quickly and tends to have an above-average Intelligence score.
The other way to think about it is that the mage’s intense focus on studying magic gives them less time to study other things, hence the slower acquisition of proficiencies. It does break down a bit logically if you think about the amount of time needed to practice weapon skills that should pretty much balance fighters (and other martial types) with mages, but it makes for a convenient excuse.
Only if you decide a priori that one’s magical skill and martial skill should take the same amount of dedication to increment. Since magic is totally not real, you could just as easily decide that magic takes a lot more dedication. And that explanation has the bonus of justifying why arcane characters gain class proficiencies at the slowest rate.
General proficiencies accrue at the same rate for all characters – 1 per 5 levels. INT increases number of general proficiencies.
Class proficiencies accrue based on saving throws as a purposeful balancing factor that favors fighters and fighter-types against mages.
From my personal experience and talking to others, it’s really quite difficult to sustain intense physical training more than twenty or thirty hours per week, and a good way to get injured - but academics can be studied 40-60 hours a week.
YMMV of course, I haven’t talked to e.g. special forces soldiers about this - this is based on college athletes, professional dancers, PhDs, and the like. I think the injury rate among special forces soldiers during training is a pretty high, however.