Felt like a good time to post something more analytical. And with the introduction of Legendary Claude, ranking the legendary and mythic heroes in FEH seemed appropriate. This "tier list" is gonna be far more simpler than a more ambitious project I got brewing, just wanted to share how I value these heroes.
Heroes are ranked from best per blessing being on the left to the worst on the right.

Comments (9)
I'd personally switch the placements of Eir + Freyja, Lilina + Edelgard, Roy + Hector, Seliph + Grima, but otherwise this is a pretty solid tier list
I personally think Seliph should be a bit higher in the rankings, as well as Dimitri and Altina. Imo though
Leif is better that Azura :joy:
I definitely disagree with your Grima, Lyn, Tiki, Seiros, and Thrasir placements but this is mostly accurate if you're basing this on Arena/AR usefulness.
Reply to: UltimatelyUnlucky (Down With BEvilgard)
Grima is sorta in the same boat as seliph due to a really outdated statline, her best stat outside of HP is 35 and is not a threatening presence on the battlefield what so ever. Not to mention she lacks a duel to keep her score relevant and her unique skill that allows her to not be weak to bows will be taken away if she does eventually get a duel which gives her the exact same problem as Tiki. Grima is definitely the worst earth legendary by a long shot, her colorless nature doesn't save her from being underwhelming on the battlefield.
Lyn while yes she does score a little higher than Hríd, it's not by much, only 2 points at max investment, and that's with a duel, but I will give you she scores a good bit higher than Gunnthrá. However of those three she's definitely the worst in combat due to a wonky bow and skill that don't end up working too well together, though you do have to replace one for duel but the bow isn't really that good, the Nifl siblings can take advantage of their prf skills to actually be useful unlike her.
Tiki does have the dual weakness, won't deny that and it is rough however she scores just as high as new gen legendaries due to having 180 BST so I'd definitely bump her up a bit just for that.
Thrasir I will it isn't quite the force she used to be but unless Naga's divine fang becomes so irrelevant that she's no longer worth using, Thrasir will always have a place on defense and she's basically the anima equivalent to Bramimond, they have different counterplay but do the same job of being a nuke mage. While I would give brami the slight edge due to being colorless, it feels hypocritical to place one and the top and one near the bottom when they're so similar.
Reply to: UltimatelyUnlucky (Down With BEvilgard)
Duma has more utility than thrasir purely because Upheaval is still good but he's a terrible combat unit.
Serios's current niche of enabling the 7th slot will become irrelevant as more mythics come out who do the same thing so I believe you have to look at what she brings to the table in her skills and the answer is nothing overly spectacular, combatively speaking she has a weapon that hard loses to NFU which is very common for a carry to use in AR. She's a dragon in anima who has to deal with Naga's existence of making Dragon's lives hell. Dragon wall would be good if she could take advantage of other mythics buffs but since she can't and people's offensive carries usually are max invested and a Res boosting astra mythic will make its way into the game one day, her damage reduction become fairly irrelevant. Her C skill only works for 5 turns which leaves you 3 turns with a dead C skill. Realistically speaking she's going to fall off real quick the minute another 2nd gen anima mythic drops and we'll all forget she ever existed.
Reply to: UltimatelyUnlucky (Down With BEvilgard)
Oh and one final thing I forgot to mention is that Marth, due to R Duel 4 and having a prf B skill, actually allows him to score the same as modern legendaries as well so I'd give him the edge at least over Hector and Roy.
Generally agree in an AR (Mythic) or Arena (Legendary) context. Would definitely rate F!Robin lower, though.