I’m not sure how the funds rating works exactly, but using up 50,000 worth of gold to promote is definitely a hinderance since most everyone else requires only 20,000. And yes, Dart >>>>>> Farina. No argument. Dart should be middle of Low at the absolute worst.
Lucius > Canas because he comes earlier, can double, can occassionally evade, and has decent supports. Canas’ support options blow outside of Pent B. His speed is low, his offense isn’t that great, he can’t dodge due to low speed, luck, and really heavy tomes. Outside of Luna, Canas doesn’t have much going for him. Oh, might as well throw in the fact he has E in staves at promotion. Bleh.
Lowen’s real advantage is his tankiness. He’s very durable, with top notch HP, Luck, Defense, and Resistance (for a cavalier). I do agree that Sain is better than Kent, mostly because Kent’s lower luck basically nullifies any durability advantage he would have gained over Sain (Even with lower speed, I think Sain wins in Avoid). I don’t, however, think there’s a big gap between the cavaliers. Since I use Sain almost exclusively, I can’t really give a strong argument for Lowen via empirical evidence.
Bows don’t really do that much more damage than other weapons to flying units. Weapons effective against a unit type have the weapon’s might doubled. Bows have low might; worse than swords. The damage advantage you’re getting from an archer isn’t that high, unless you use a heavier bow, in which case you risk losing double-attack advantage.
For Hector vs. Eliwood, it’s mostly an issue of early game vs. end game (Hector rules early on, but Eliwood does outclass him towards the end due to movement and level lead). Since the early game is harder, I actually can see Hector being just above Eliwood. I just don’t remember Eliwood’s mid-game performance in HHM.
Guy gets good support options to fix offensive problems he has early on (Matthew being the best, Priscilla’s a good option too). He’s also evasive as hell. Weapon Triangle does hurt him, though, since he only has one weapon type. Honestly, I haven’t used him much, so I can’t remember exactly how good or how bad he turns out.
Serra does have the advantage of a six level lead over everyone. She’s the first one to promote. Always.
Nils/Ninian have good evade, but no defense, so yes, they’re frail. Just that their ability to give your best character a second action on every player turn is just too good.
Matthew is absolute #1 for one reason only: Silver Card. Nearly required to five-star Funds, and thus nearly required for an S-rank.
Slayer Rings and 
