I've played this MU a good handful of times but only in tournament. And it's by a top placing Fox in Michigan. So I've had to learn on the fly.
A few notes:
-When you're at kill % shield is your safe place. Don't just sit in it, but don't be too afraid of getting grabbed. All that will come out of it is damage, unless you have trouble landing vs him. I suggest learning how to b-reverse gyro cancel if you haven't mastered that already (you def should).
-Most of Fox's kill attempts are overcommitting. So if you do shield one of his overcommitting options, learn how much of a window you have to punish, and plan out how you will punish him.
-When in the jab combo, keep smashing both sticks up, and when high enough, begin to up b away. If the fox doesn't catch on, you will get out. He might get in an up air. He will get a up smash if he's mindful of it. But at least this ends the pain a lot sooner. Don't let him jab combo you where you'll be potentially combo you all across the stage. Be very mindful of your positioning for that.
-I generally love battlefield, but I do not enjoy the up air opportunities it grants fox.
-When fox is up b'ing from below the stage, be mindful as to whether he has a habit of up b'ing straight up towards the ledge, or does he up b into the stage at a slant and ride up it some? React to both. If he's up b's straight up, just spike him. If he up b's into the stage, the spike timing is a little tricky. you might be better off with a turn around gyro towards the stage or a well timed bair. Just find your niche in that situation and dominate with it.
I think if you're mindful of how hard it can be for fox to kill if played correctly, I don't think it's too bad for rob. maybe even MU. But I don't see it worse than 45:55 atm.