1. Sheiks Sh going over lasers isnt all that useful. Her aerial mobility is garbage, and her downward priority is generally also pretty terrible. If sheik makes it her perogative to sh over your lasers, lol, you could place uptilt, bairs, sh rising dairs, almost anything in her way and **** her he balls off. this is more of a negative than anything, because s jumping sheik is the ****-bait
2. Tru about the DD. is her WD oos really "faster" ? interesting, i dont know the frames on their jumps.
3. debatable, but i think its marth favor reason i'll describe in a longer post when i have more time.
4. sheiks nair is 6 frames. Marths fair iirc is 8 frames. but i think what you might be saying is that it technically takes time for marth's sword to arc from over his head down to hit you so i see your point.
5. I feel like marths relative ease/reliably at low percents, makes up for his lack of high percent combo/ko moves. Its like a tradeoff. sheik has trouble building damage with hard techchases at low percents, but easy combo into kill moves at high percents. Marth is the opposite. but i feel like its ok for marth because once your at that kill percent, he doesn't need to combo into a kill move anyway, any random hit that sends you offstage and then he just trusts his edgeguarding.
as an aside, CC'ing is far more effective vs sheik at useful percents because of the way both of their movesets work.
so idk, those are my thoughts. I'll make a longer posts about how i feel about their gimping ability later tonight when i've got more time.
so yea, overall, i think marth is the harder matchup personally