Roy is total dogwater. If the bracket was 100% foxes then he might have a chance to just cheese them all out and chaingrab them to death, sure. But floaties just annihilate him. The puff one hit kill is a stupid meme option because it only works on a couple stages and is insanely hard to line up consistently (I'd know, people try to counterpick my gnw with roy all the time lol) All the puffs would have to do is avoid yoshi's like most people avoid FD against marth.
His combo game, recovery and kill options are all insanely worse than marth's. His aerials can be cc'ed until forever, he just struggles so freaking hard to get anything done. If zain decided to main him starting now he'd probably do ok and make some top 8's because zain is a monster, but like a different guy said in this thread earlier, winning a tournament is REALLY hard even with marth. Doing it with marth's dopey mediocre cousin is a nightmare.