Tbh, i disagree. Sure it may seem like it, but Marianne and Bravekeeper are the most future-proof since their niches are impossible to replicate, while Marth and Eirika will eventually fall to the next big Sword Infantry and Lance Cav. Sure Marth has a Yu-gi-oh weapon and Eirika wrecks stuff. And? Do they brings anything new to the fast sword infantry archetype? B!Alm for example has the tempest effect and has both windsweep and NFU on one weapon and B!Eliwood is one of the few cavs that have dodge, and is just as capable of using Canto as Eirika. Meawhile Marianne is a dancer that cant be foiled by Duo Hindrance or Isolation, doesnt suffers the BST penalties of dancers and is a really good combat unit even without her pref special (while Marth is totally dependant on Shining Emblem to stand out) and Gatekeeper is the only unit that nullifies warping effects, his weapon is a really good support, and for a mage, his statline is really unique, and you can use him as a tank or a support depending on your needs, again, unlike Eirika, who can only be a PP nuke and is relies in Moonlight Bangle to not be another Player Phase Lance Cavalier