I think Kellam is a touch too low. I'm not entirely sure how he fares as a unit, but just the fact that you get a +5 defense support right off the bat means you can literally take him into chapters for JUST that bonus. The +3 strength boost isn't bad either.
I feel like Sully and Stahl are too high. Granted, I didn't use them as much as some units, and perhaps I just got unlucky with their growths, but they just fell behind the rest of my team.
I'd bump Cherche up to A tier. Yeah, her speed is bad and you need to watch out for any mages, but her pure strength and defense are amazing, and she's perfectly usable as soon as you acquire her.
For that matter, I'd put Sumia-Lucina higher too, Parallel Falchion is arguably the best sword in the game with its combination of availability, unbreakability, and sheer power, and she ended up being one of the few units that I could actually count on to reliably evade things.
Chrom I'd also drop a spot or two. He's a good unit, don't get me wrong, but Lucina and the fliers ended up being a lot more useful in my playthrough.
And for that matter, Olivia should go up at least a tier or two, I know that galeforce exists and the enemy phase is insanely important this game, but still, she's a dancer.