I love marth and will probably use him quite a bit in smash 4. However I shed no tears for his current position, mostly out of fear that the wrong buff could easily turn him into a character that invalidates most of the cast again, even if he still has tough MUs among the better members of the cast. I also wonder is he really in need of improvement? Or has he just not been fully developed yet.
He never invalidated anyone by himself tbh, beyond the silly grab release/oversight stuff.
Right now what it feels as if its just 'harder' to do things compared to other characters, most characters can sh auto cancel aerials with multi/longer lasting hitboxes or sh rising ff aerials with auto cancels. Marth doesn't; neutral air auto cancels frame 44 and it ends on 21, fair has no auto cancel, uair/bair auto cancel with just minute alterations of timing on rising aerials. It feels like a very very odd limiting to the character that hurts just about everyone's first impressions on how to use the character well. Everyone says the same thing "clunky" "slow", and I know fully well how to work around them, and at the same time I know some 4-5 frame differences here and there on ACs will hence time out well/properly with many use cases.
But I don't think he deserves structural buffs like say Ike got, he's close to being "just right" without being dominating or underwhelming.
Marth's short hop is 41 frames in length.
His aerials are basically all the same frame data, fair is only 3 frames laggier on ending; it's just there's less time in his jump than in Brawl/melee. If he stayed in the air for literally 1 frame longer he'd have fair -> uair and be in a completely different boat in terms of capabilities I'd say, 2 frames and it's double fair again. There's purposeful limiting here.
His Sh FF is 24 frames. His bair auto cancels on 32, up air on 38. Nair I suppose is designed to be easily timed into a sh rising -> ff with minimal 'down time' but it's still a 3 frame down time. Honestly, in comparison to Brawl (throughout the entire game, not just Marth) Marth's auto cancels do not make sense nor flow. In nearly all cases, Brawl characters had meaningful timings with their aerials auto cancels that owed themselves to learning the timing/best use cases.
(Like MK can sh ff fair that auto cancels in such a way that he can use it in between falco's shdl and land into shield fine, covering the side-b and not overly exposing himself to laser damage [ZeRo's way of playing the matchup]).