As I said before, one of the problems with the Oli glitch is how it makes certain characters fear him more than they should. You have a character who has a projectile that latches onto you and does constant damage that can rack up very quickly. Your answers to this are: don't get hit (which can be hard to do), knock them off with an attack (which doesn't always work and requires you wasting time and leaving yourself open to further attack), ignore them and take the damage or reflect them. This glitch effectively gets rid of one of those options, one of the better ones too since you don't take damage and you possibly inflict damage on Oli. If you try to reflect his Pikmin Throw, he can get access to ohko/high damaging aerials and throws, kinda like if Ice Climbers didn't need to do numerous throws to get a kill and if they had ohko aerials. Keep in mind that Oli's side special isn't the only thing he has that can be reflected, all 3 of his smashes can too though that's risky to do.
If we get rid of every reflector possible here's what characters are stuck with:
Impact Orbitars which are garbage and a countering side special (pretty sure the other two reflect, at the very least the default does) Missing out on a decent ko move, least for Pit.
Shocking Cape which isn't too bad. It kills but it has bad startup and isn't a gimping tool like the other two though gimping Oli with it probably isn't too effective in this game unless he has 3 Pikmin with him.
Reflector Void which honestly isn't that bad. My preferred reflector most of the time anyways.
Thankfully Leaf and Plant Barrier are good moves already and can probably deal with Pikmin better than Skull Barrier.
Absorber is useless but at least you get Bomb Drop.
A counter or what is basically Wizard Foot/Falcon Kick. Much like the Mario's you miss out on a gimp tool though.
Angelic Missle or, ya know, Super Speed...doubt there's a complaint there.
Nayru's Passion which from what I've read is just plain bad. You also miss out on a move with invincibility frames.
And then these three characters have to have a reflector. Doesn't matter too much for Fox since that's the only use for his Reflector in this game anyways but I'm pretty sure R.O.B.'s Arm Rotor has more use than just being a reflector and as for Ness...it's a smash attack.
Another thing to consider with this glitch is that some tournaments are going to have 10 presets and that's it. What if there isn't one with Nayru's Passion or Shocking Cape or Impact Orbitars etc.? You could always just not use the move I guess but again it makes Oli more threatening than he should be.
TL;DR The Oli glitch is a problem for certain characters in singles but aside from 3 characters, all of them have a means of avoiding the problem although the answer isn't always that great. Makes Oli more of a potential threat than he should be to certain characters.