I don't understand what you mean by a hokage being able to use everything, I said it wouldn't increase uses, a character can have all the abilities, but will not be able to use them until their level gives them enough uses (example, a level 1 with 19 intelligence gets only about 6 or 7 uses) so they wouldn't be able to use level 18 jutsus until level 10 or 11.
also, at 2 oro kills to 1 specialty point, that would be 36 oro kills without spending points on any other stats. that means base stats in everything if you focused on this, surely that would put some kind of a dent in their performance.
as for the mount problem, maybe a stat requirement on mounts? maybe you need so much intelligence and wisdom to summon the mount each day. Or maybe it costs X chakra a day to summon it.
finally, if it were put in we could change everything, like everyone starts with the level one of every specialty that there stats allow, but doesn't gain specialty points at level ups, just use points. then you cannot ever use a level 18 genjutsu specialty unless you spend 36 oro kills on genjutsu.
but I do see flaws now that it is pointed out, It could work if the all or some of the specialty increses by special events were removed or switched to only increase uses (not specialty points), but that could take a lot of work.
could someone please clerify what the problems you all see are?