yeh.
we can't fully judge your Marth if you're playing mediocre -> crap hole players. No offense.
That ROB didn't know what he was doing, he didn't know the match up... and so forth.
learn your spacing. and learn different approaches. You spammed fair, and you did double fairs too often... it wasn't pretty especially since you didn't hit or shadow hit him. (and shadow hitting isn't even good)
As junk said, Marth's grab game with the exception of those with a f-throw (chain) or death combo. and grab release combo set up... is poor. Shield grab only. If they get too close and lag cause you shield or even better perfect shielded, well grabbing is a good way to GTFO.
Don't shieldbreaker unless you notice your opponent shield a lot, and you've connected a DB combo or a Fsmash to their shield. THAT IS THE ONLY TIME YOU SHOULD DEPEND ON SB.
Short hop. please.
When you Fair approach, DI AWAY FROM THEM... don't follow up. they will punish you.
on occasion weaken their shield first and punish them, since they won't want to use their shields for a bit.
the counters you performed were pretty bad. Don't counter early. Counter comes out pretty fast, and correct me but it comes out as fast as invincibility frames from AD... so yeah learn to time it.
learn to dtilt and dmash, rather than spamming fsmash. in the zelda match, you only dtilted when it was useless and ??? iono why you even did that. EDIT: so in the ROB rematch you quit spamming Fsmash... and replaced it with dtilt. it was working, but that ROB isn't that good. still didn't get better.
dtilt can be viable and followed up my DB. or what ever is appropriate.
DB up is reliable to combo, if you didn't know. DB down, is good for edgeguarding, and DB neutral is overall reliable for knockback off stage.
In the 2nd ROB match and other matches, you used Nair pretty well. tipped a lot of them.
Learn spacing, more approaches, and set up. You do about 5 moves. Oh, and WALK MORE.