fox isn't going to win by drill shining and grabbing all day long. if the roy is competent. drill shine doesn't lead to anything except maybe some chasing, and takes like fifteen damge. he eventually will have to throw out an attack than can be CC'd. then d-tilt, f-smash, edguard. and assuming the roy is a competent player he will know how to bait his d-tilt, which, i dont know if you remember this, it automatically leads to roy's strongest move, which sets fox up for death at very low percentages. Fox can be at 20%. d-tilt, f-smash, edguard, death. Fox doesn't kill Roy that quickly.
in contrast, fox can drillshine, wavedash, upthrow, upair, (and possible one or two more upairs) Marth, then do it again and marth is pretty much dead.
Roy edgeguards fox as easily as marth does, with d-tilt, to f-smash. Roy's not a good character at all, but he can own fastfallers.
hey maybe its just my roy thats better than my marth against Fox. seems unlikely