I think Lyn's realiability would been higher if she could use the Murgleis. I've played FE7 a couple times and I NEVER use the Sol Katti on her, even less with the final boss. Why would I even use a sword which weighs her down like she was carrying a wyvern on her back? She's already pretty frail so why handicap her more? I'll just stick to the Mani Katti-Killing Edge strat and make her stand back when the dragon appears.
Bows seem a really good idea for her, both gameplay and lore wise on my eyes. They help her dish good damage with high crit chance and it makes sense for her backstory considering she's a nomad and, well, nomads hunt a lot.
So yeah, an actual Legendary class weapon would do wonders on her rather than pulling out the #23 mcguffin just so she doesn't feel left out when granda Athos brings toys for everyone. Like that she could deal some ACTUAL damage to Nergal and the boss the weapon was designed to fight against and likely double it (something she's good at because remember, she's basically a Myrmidon).
And finally, that would've make her stand out from the other two lords as Hector wields a giant axe like it's made of paper, Eliwood receives a big flaming sword and Lyn... she gets a sword with a "meh" rate design and a backstory no one knows. A very dissapointing deal for one of the main characters of the game (and my favourite waifu of all the FE games)