Marth's fair: +3 frame start up, +3 frame end time. Still literally the same beast as it was in Brawl while completely in the air.
Dair: +3 frame start up, I think 10 frames taken off the landing.
Uair/Bair/Nair: Same as Brawl.
Auto cancels and landing lag? Bair is the same as in Brawl, all landing lag is generally worse for the ENTIRE CAST.
Jab: +1 start up
Dancing blade: +3 start up, a lot laggier ending on the first strike (but not when used in the air, only on the ground, otherwise same ending as in Brawl).
Marth forward smash: -1 frame start up (as in, faster), something like 5+ frames taken off the ending lag.
Up Smash: 2 frames extra start up (on the feet hitbox, sword 'start up' is still the same)
Everything else is either the same start up, with negligible ending differences or
buffed.
P.S. I still main Marth. Won a live/local/in person tournament with him yesterday
"guess I'm not playing Marth"

When I say 'objective' I mean it. Frame data exists for both characters already, take a look, or stay ignorant and cry about your inability to use a
hard to play character. I haven't seen you around the Marth boards, you should set yourself up to be liberated.