dude be quiet u dont know what ur saying. its way easier to tip a smash than it is a nair. his fsmash can kill and is his quickest kill move. especially if u tip. but there is a reason it is so low.
No, your knowledge of Marth is lacking.
Tippered f-smash is a -40 frame advantage on shield, untippered (which can't kill) is -32. Shield drop is 8 frames, and Ike's foreward smash is frame 29, just for reference.
Yes, I'm telling you that if you hit shield and you tipper the f-smash, you get hit by an IKE FORWARD SMASH. That's how unsafe it is. Also, Marth leans forward when he does it, meaning that moves that wouldn't be in range, ARE.
For a lot of players, 10 frames is too fast to react, but that the top of the metagame, it can be shielded on reaction.
It's tippered kill percent is impressive, yes, but the second hit of a tippered nair is very good too, and is a lot safer.
As for faster, up tilt is frame 7, and kills at 104 (114 for any hitbox). Downsmash is frame 6 and kills at 98. Nair comes out at frame 6 too, dunno the actual kill percent, but it's quite low (not as low as tippered f-smash).
OOS (which is pretty much the only time you should use Marth's kill moves) , pretty much the only kill move marth has which is slower then f-smash is upsmash. Oh, and charged shieldbreaker.
Overall, nair>>>>>>>>>>>>>>>>>>>>>>>>>>>>fsmash.
Honestly, just about any of marth's kill moves >f-smash, it's just not good except in combos or when you have a guarenteed 10 net frame advantage on your opponent.
F-smash sux.