Godlike
Dheginsea (10) vs Cainaghis (10): Honestly, I'd think most sane levels of boss scaling should give this to Cain. He does 32% of Dheginsea's HP in-game at base level with no supports or Blood Tide (with those, more like 44%), while Dheg only 3HKOs him back. I mean, yes, Dheg would win solo in-game of course but yeah, any reasonable scaling tilts this.
Nailah (10) vs Naesala (10): Naesala doubles, which is pretty hard to recover from. Nailah does win almost every stat that isn't speed, but it's probably not enough.
Ashera (10) vs Tibarn (10): Um yeah, he needs nine turns to win this as far as I'm concerned. Ashera pretty much auto-beats everyone in FE since they're so ST-focused (excluding a couple other bosses who are worse versions of herself!) so prepare for boringness, at least she had a good fight last week which I didn't even bother to math out!
Dragon (7) vs Athos (7): Depends entirely on if I let Dragon avoid counters. I think Athos misses the OHKO, but certainly has a 2HKO, so if Dragon doesn't avoid counters, then Athos sits, counters, then kills. If Dragon can avoid that strategy though, it wins.
Heavy
Roy (6) vs Ashnard (9): Both of these guys are headaches. Kneejerk is Roy though, Ashnard HP is some shade of hideous.
Rutger (6) vs Ephraim (8): Decent fight probably, since Rutger is so fast he doubles. Still, weapon triangle is a huge concern here. Thinking.
Nephenee (9) vs Eirika (8): Like the above fight, one doubles and the other has weapon triangle. However, this time, the doubling one has better stats anyway.
Elincia (10) vs Hector (7): Quads, and has weapon triangle unless Hector picks up a sword which makes him notably worse. Hand Axes are out, which means Stun's going to be a pain regardless.
Middle
Marth (11) vs Colm (8): Not much respect for Marth. Colm has actual evasion and I bet most of his stats end up better since I don't see Marth as high-levelled as the stat topic.
Marcia (9) vs Oswin (7): Thinking that if he could beat Jill, who has generally better non-speed/res stats (and doubled anyway), he can beat Marcia.
Canas (7) vs Micaiah (10): Weapon triangle advantage means she always hits while Canas struggles, has Nosferatu, probably doubles if Canas goes for Nos himself, and her overkill luck negates the strategy of praying for Luna crits. (EDIT: Never mind she doubles Canas if he goes for anything other than Flux. That makes things more ugly.)
Oscar (9) vs Lute (8): I -think- Oscar can 2HKO with Javelin -> Silver kill. Or Lute may fail to 2HKO. If either of these are true, I'll be voting for Oscar because move/canto concerns leave him winning tiebreaks to me most likely.
Light
Innes (8) vs Gilliam (8): In a battle between mediocrity, assume the one with a very high functional defence stat has the edge.
Sanaki (10) vs Lethe (9): Well, Lethe nulls her usual fire weakness, which makes this actually interesting! Lethe's damage is very poor but she probably doubles and Sanaki has bad durability, so hmm, unsure. EDIT: No doubling? Well then.
Oliver (10) vs Soren (9): Soren doubles because Oliver speed is a thing, but he does have Nosferatu which could tilt a slugfest. Uncertain here. Weapon triangle and Adept may make the difference, sure.
Pain (10) vs Volug (10): Pain has 26 attack against stats... hmm. Eyeballing things, average durability should be about 7.5 Def / 23 HP, so Pain does 80% per hit. He has 10 speed to an 11.5 average. Durability is some shade of bad being an FE boss. Volug gets one-rounded untransformed, while halfshifted, he is probably just 2HKOed. He can bait Pain to attack him so he 2HKOs first... if he does. Okay, let's try to figure this out. Volug does about 62% halfshifted with a double, to me (different people scale FE damage differently). Considering the 6 fighters you have, assuming steel or +3 iron forges (same attack), damage done to Pain is... Edward 6, Leonardo 7, Nolan 12, Sothe 11, Aran 9, Meg 7, so an average of 8.7 or so. That puts Pain at about 57% pdur by my scaling. Huh. Was not expecting to vote for Volug, but there you go. Pain's a weird Light FE, amazing damage but shit durability.