I don't get what you mean here. How does noble troops being very common make the game more fun? From what I and others here have seen, all it does it make the game less interesting and less fun.
The problem with that theory is that the AI doesn't artificially restrict themselves on what troops they hire.
If you choose not to hire elite troops in order to experience a more varied army composition, you're putting yourself at 2 disadvantages to the AI - you get less recruits per village visit, and you get objectively weaker troops. The game is grindy enough already without handicapping yourself like that.
Also it just isn't fun for players to have to artificially restrict themselves to make a game more interesting.
Far from giving the player more options, flooding the villages with noble troops actually gives them less options, because noble troops have a totally linear upgrade path.
How does it ruin your game to have noble troops in sensible quantities?
The thing that's meant to balance Vanguard and give you a reason to recruit them is that Banner Knight recruits are uncommon, so in order to have a decently sized cavalry contingent, some of them would have to be non-noble cavalry to complement your noble cavalry.
This would work... except for the fact that Banner Knight recruits aren't uncommon.
Because example I am playing as vlandia, I want full force cavalry 7.0 at least on world map speed to keep going in early of game right off bat, and It's seem only noble offer that right off bat, while normal troop don't offer that in right off bat, and you spent more time seaching mount to get what you want for troop. I rather hunt bandit than search mount to get troop to be cavalry, I'm not interested in foot soldier due it's slow down world map, unless there is perk bouns that help world map speed, but that is take lot of leveling and perk to buff world map speed for footman.
I do not like grindy and handicapping as well, but problem is not noble available but normal troop are handicapping, normal and noble is just same people, expect noble gettting nice equipment at start, but in the end, noble and normal troop are same, once normal troop get good equipment just as noble do, it's just take longer, and show normal troop just as good as noble, but that issues, way game design, normal troop should be buff little more especially in late line or final line of normal troop, they can be elite troop and fighting way better than noble in the end, since they been in battle longer, in real live, often king or higher rank lord promotion warrior who are good at fighting into noble stats from lower class, not always in battlefield, but sometime normal class help or new idea or buff kingdom's economy got promotion, something unique to king or kingdom in good way.
So I think normal troop should be more deadly at end of line while noble is good at start out, basic. it's make sense since normal troop do in battle more than lord, and each time battle normal troop getting wiser, experience, even troop might or might not get rich loot, king or lord would gave best equipment due seeing how good warrior alive and loyal after many battle in case still poor in many battle.
So I think it's would be good design, noble might good at start out, but normal troop at end of tree is little bit more deadly than noble at end of tree, elite don't care normal or noble, but excellent skill in fighting, Just suggest, noble and normal lead to top special elite, whatever normal and noble, just idea, thought. Noble while may be uncommon, but still common enough, even thought normal people is common but better word for it "abundance" while elite is rare, master of craft few, basic good and bad skill is common, so go on.
I think issues is way troop tree design rather, normal troop should be buff, I think in real life veterans normal troop fight better than noble one in the end so it's should be buff on normal troop more than noble at least on end of tree line, more or less.
Noble is good start out, while normal troop should be better at end of tree line than noble.