Legendary in Weapon Armor or Perception

[LostSoul]

Is it possible to get Legendary benefits for the above areas outside of through particular classes?

[HammerJack]

No. That progression is, as far as I can tell, intended to be a major part of the chassis of the class, and is not something that can be picked up on the side.

[Claxon]

Proficiency progression for weapons, armor, and perception seems to be tied to class advancement only (for getting proficiency beyond trained).

There are abilities that tie your progression with specific things to your other class progression. Such as the Human feat Unconventional Expertise, but such abilities are pretty uncommon as far as I can tell.

Usually as a feat you can just pick up Trained proficiency and it never increases.

Which does mean that picking up trained proficiency is basically worthless, at least in my opinion.

Personally I think Armor Proficiency should give you training in the next tier heavier armor, and tie its progression to your class progressed armor proficiency. So if you had unarmored proficiency only, you would get light armor and would have the same proficiency as your unarmored proficiency. Light to medium, and medium to heavy. Considering that all unarmored, light, and medium armor all have the same potential max AC (and the difference is purely about dex investment) it seems fair to let the proficiency for all of them scale together. Heavy armor is better by 1 point of max AC bonus, but Champion is the only class that gets Legendary Heavy Proficiency (I think). So even if you had a character that was Master in Heavy Armor because they picked up the feat (and had master armor proficiency progression on their class) the Champion still has the best AC.

I think similar things should be done for Weapon Proficiency, though instead of simple weapons growing to trained in all martial you would choose 1 martial weapon but your proficiency would advance the same as your simple weapon proficiency.

[Megistone]

I agree with Claxon (yes, I'm spamming a bit about this topic).
Only thing, I'd make the martial weapon training feat give proficiency with a weapon group instead of a single weapon: we've got that classification, but only fighters are using it at the moment.

[Ramanujan]

It appears from the little that’s been discussed by those that have the World Guide PDF, that training in X, will be a common prerequisite for dedications, at least for those that used to be/would have been Prestige Classes in PF1.

Which might help explain the existence of those feats... as a feat tax only some classes need to pay, assuming they don’t get it via some other dedication first.