Well that's some misinformation on Marth.
LordShade67
ZephyrZ
Poor animations don't make a character bad. At all. It's the hitboxes that matter. If Marth's animations were shrunk to match the hitboxes, his viability would not change one bit.
Marth's issue is not neutral either. He has very quick, long-ranged, and safe pokes (Both in the air and on the ground), coupled with an excellent walk for microspacing fundamentally makes for good neutral.
Marth's issue is that his good neutral leads into neutral. You hit a D-tilt? Great! Now you only need to hit another 10 before you could get a kill. Try not to mess up and eat 30%, K?
THAT'S his issue. The main thing that he does well in during advantaged state is edgeguarding, but he's still outclassed by many at that and recoveries are so good anyway that it doesn't matter much. The reward is just not there for winning neutral.
Take someone like Cloud. He can be played similarly to Marth, in the sense that he can space around and control space with his disjoints (albeit not as well as Marth because of poor ground spacing options). What makes Cloud good is that he can convert off of safe pokes like his Nair into long, damaging combos.
We can see this type of thing in most top tiers in many fighting games; being able to combo off of pokes is an amazing thing (in this game you have stuff like Sheik Fair, ZSS Nair, Cloud Nair, Mario Bair, etc.). Marth just doesn't have that.