That little bit of RNG is something that I've both resented and appreciated as a staple of the series, because sometimes your efforts are squandered, and sometimes you hit a jackpot, but overall the stats averaged out, barring extreme RNG bad/good luck. Giving all characters infinite level ups removed that moment of excitement from leveling up from the game, ontop of the thought and care you'd normally put into carefully rationing the available enemies to level up your guys, because in the end it doesn't even matter, your characters, all of them, are destined to become godlike. The only thing the game asks is the time investment spent grinding, then re-grinding your characters. Even if it's entirely optional, I feel the game as a whole was much poorer for simply having it included.
Just... Don't infinitely level them? There's nothing saying you have to do it?
It's simply my belief that even if something is purely optional, if it threatens what is obviously the primary engagement that the game is built around, then that optional thing actively detracts from the overall enjoyment of the game. I'm reminded of the Final Fantasy 7 port to PC, which explicitly allows you to cheat. You just have built-in cheat codes you can use to overcome basically whatever obstacle the game has. Now those cheats are optional, obviously, but just their existence is de-legitimizing the actual draw of the gameplay. It's like the game designers themselves are poking their heads through the computer monitor, and telling me themselves to not enjoy their game.
Actually, this reminds me of something else I want to talk about, that I'm actually REALLY on the fence about: There's free bonuses tied to the Social / Online Game Mechanic accessible through the crystal ball, atleast as far as I've explored it, it does give you free stuff, but it's just small stuff, that is one time, and it's not gamebreaking. Like, there's a bonus for purchasing both Conquest and Birthright, but it's some class change stuff, and two different stat enhancers, plus some more for when Revelations comes out. I'm extremely on the fence about that, cause it's not significantly game changing, but it's a purchased bonus, which is really hard to justify in my mind.
There's also bonuses for visiting castles, you get Dragon Vein Points to help you furnish your castle, plus the very act of visiting castles gives you access to weapons and staves that are simply not available in your route. I.e. you can purchase and upgrade Hoshido items while playing Nohr, and vice versa. Plus you can acquire more free gems and food. And while I wish that off-route items simply cost more, it feels alright because none of it ever adds to your main finite resource in Conquest: Gold. Everything still costs gold, which remains finite and valuable, so this perk isn't game breaking, but it's questionable.
The last thing is there's bonuses for visiting a lot of castles and battling players, so if you visit like 10 castles, or if you battle players, you get some free items that are redeemed from a list. They seem like really inconsequential items, but then again this list of free items is huge, and the possibility of grinding out visitations or battles to gain access to more of these items is possible, but the sheer number that you'd have to grind out makes it seem very unfeasible unless you've backed yourself into a very bad gamestate and you need every advantage you can get just to proceed with the game. Once again, I'm on the fence about it, in that it seems like it's fine, but there's still some friction with my personal game design scruples.
EDIT: But atleast it's not Awakening, which was just overt BS "Here's some free legendary weapons, have fun!". That was just garbage nonsense explicit cheating. God I can't shit on Awakening enough.