So one thing I've gotten the impression of (it didn't matter much in Sacred Stones since it's baby easy) is that leveling up is random and it's very possible to have characters become useless as time goes on due to bad levels.
Is that the case?
What about my Lord? Can he end up being shitty or are stats weighted for him? If he does end up being shitty what do I do?
Also is there anywhere with a clear description of the math involved? The previews are useful but I can't preview what'll happen when a dude moves on me.
Random levels and stats has been a staple feature of every FE to date. It's very possible to end up with a crappy main character, but unlikely due to how naturally good her stat growths are. If you end up with one or more characters screwed by stat growths, it seems the game gives you a LOT of strategic options that help to mitigate randomness and the effects of bad luck, like pairing up since the bonus stats on pairs is static, so having a crappy partner isn't that big of a deal. But the game also just straight up gives you a lot of characters, so getting bad stats on a couple characters is possible, but getting bad stats on ALL of them is improbable to the extreme. If those units DO fail you though, you use captured units, children units, copied units, einherjer units, there's honestly so many options it's hard to see a player backing themselves into an unwinnable gamestate.
Also, since it's possible to earn Support points fighting in other people's castles, it's more than possible to grind those out, get S rank relationships, and unlock paralogues, which do give Experience and awesome new characters to boot.
but FE math is always really easy, just look at your defense, and the opponent's attack power, and add/subtract. Just be sure to add in environmental and skill bonuses too, and you're good. Dodge rate is significantly harder to calculate in your head, but just trust that the opponent's RNG will always roll well, and you'll make very few strategic faux pas.