As game progresses, fewer skilled people at the court

I will agree that stats go down over time, though depending on the the start date you start out sometimes you dont notice the difference as much since while rare some 20+ do generate and wander around doing things, while there aren't an excess of OP cannon people at the beginning like you start finding in later dates with more details saying everyone is a demigod.

As for formidable fighters, you can find them on rare occasions spawned in via the warrior things, such as the marshal job or recruit soldier. Generally I'd like to see say overseas travel have a higher chance of generating some 20s or so sometimes with some interesting trait lines at least as you find exceptional people seeking a chance to bypass the political grind of their home in a foreigners retinue. While I agree that in the later bookmarks the level of power is a bit high, I think all things considered there should probably be a bit more potential recruits that spawn around somewhere between base CK2 and cannon character OP levels.

Could have a fair few events with fairly long MTTH on it, and maybe based on traits. So for instance cruel, craven, envious, etc people would generally be unlike to attract courtiers of skill who openly show themselves, since they're either not worthy of respect or may outright attack you for your abilities, while diligent, honorable, kind, etc would be more likely to fire the events every 10-20 years maybe and get a strong courtier who demonstrates their abilities from among the faceless fold. This would add a bit more variety in skillsets and may give the AI the occasional advantage they need to get things done.

While we're at it: Any chance we can give the maester a chance to train the kids combat skills based on their martial? Since they default to tutors, it'd make sense that part of the general education of most nobles would be combat theory. They wouldn't be learning outright from a maester maybe but there's a decent chance he'd teach them things from combat manuals and such get them up to say level 2 fighter potentially just on theory alone. Even girls could use some knowledge on how to break a grapple of a horny drunk and run for it before her honor is sullied. Or how to use a knife to properly slit the throat of a frey's brand new wife.

You can set your marshal to train children in fighting. IIRC the chance is based on the marshal's own level of fighting ability rather than their martial ability, so one with formidable fighter a bit lower martial is the preferred choice in this case.

I may be mistaken here, but I seem to recall that he only trains your children and grand-children. This is usually a good thing since you want his efforts focused on your potential heirs rather than the children of courtiers.

I know all of these methods you mentioned to train children in combat. I'm doing it. I think it would be awesome if other lords as npcs did it as well, though