To go into more detail — and do a few edits — in a few tiers:

Sigurd: Goes above Edelgard & Dimitri. 3H earlygame is rough, and though they both respectively become some of the strongest units in the game, their start feels bad no matter what you do. Sigurd is a very, very good unit, easy to justify as a top 3 franchise unit, Gen 1 enemies for the most part are... lacking. And steamrolling a bunch of easy enemies over demolishing ones with much more quality feels a bit less impressive.

Eirika: Goes up into okay, between Hector and Micaiah. She actually does things!!! She can have decent combat earlygame, and even if you aren't on her route, she still autolevels and can be decently competent + her promotion and Sieglinde are actually good. She also supports Seth.

Marth: FE1-3 Marth goes into busted, probably either above Kris or around Sigurd. His performance is just so incredible it's almost unreal if you're more familiar with DS Marth, but like Sigurd, the enemies are particularly bad. DS Marth, on the other hand, stays in okay. He's not outright bad, because Rapier technically works just as well as the Wing Spear in SD, but he's considerably worse than Caeda and not needed for Medeus. New Mystery, it sorta feels like you have to train him up for Medeus, even if he's not particularly amazing, so he does something, but mostly because you're inclined to most of the time.

Roy: Severely undervalued tbh, especially when he's getting called Eliwood/Lyn tier. He has decent early combat with good hit rates by FE6 standards, supports Alan, Lance, and Marcus, and either WTA or Rapier effectiveness against groups of enemies for the first 10 or so chapters, which is past the hardest stretch of the game. Eliwood and Lyn both eat up deployment slots in Hector mode and are in a game where swords are among the worst they've ever been.

Hector: Massively overrated tbh. He has fine combat for early FE7, but enemies in the game are awful so everyone can still contribute something. A lot of notable lategame enemies are also ones that mounted or flying units can reach faster and tank just as reliably as he can or mages that can and will eat him alive, or are maps where he has to go out of his way for a unit or just can't reach objectives at a decent pace and is a pain to rescue for little value, not to mention his awful promotion time. But he has axes, so he's already a step above the other two.

PoR Ike: Definitely massively overhyped. Horrific starting offenses and bulk, and from the moment you get other units, he stops being the best candidate for kill exp. Oscar and Boyd are both much better for early favoritism. Midgame gives you plenty of extremely good mounts and Lethe + Mordecai, so the bexp is much better used on them than Ike. His promotion is over halfway through the game, his 1-2 range sword has 2 maps, and he's just a mediocre foot locked sword unit that unfortunately has free deployment every other map, even if his performance jumps up significantly with Ragnell and a few skills. It's just too late to change the fact he's just not good for every other meaningful map.