"Looks like low-BST, early-route PC fodder."
-my thoughts on Cutiefly's first reveal

I am not going to give a definite opinion on whether Cutiefly is ban-worthy OP or not, because IMO the SM LC tier is still a bit too undefined and fresh (and as a result, I also do not have a lot of on-field experience in piloting it). But in the few times that I have tried it out, Cutiefly is definitely a pivotal force in deciding games. It reminds me back of DP OU: "Who can set up the Salamence first?"

Weaknesses include: Flying, Poison, Rock, Steel, Fire.

In my experience, it feels like a good strategy against Cutiefly is the threat of being able to check it, and thereby exploit its SR weakness. The Fairy-Psychic attack combo is unresisted in LC, save for Steel Pokemon other than Pawniard, so you are almost required to use a Steel Pokemon to check, much less counter Cutiefly. You would have to switch it in on the first QD, because +2 will be too much to handle. To rub it in, Cutiefly boasts a sexy 19 raw Speed stat that gets backed up by Quiver Dance, so outspeeding it is completely out of the question unless you're using like Scarf Elekid. Of course, there are different checks depending on whether Cutiefly is at +0 or +1, but due to the nature of QD, most special attackers become set-up fodder.

Assuming you are able to switch-in on +1 Eviolite Cutiefly without eating an attack, you might be able to beat it 1v1, but even if you do manage to defeat it, it won't be without repercussion. Cutiefly has a small chance to OHKO non-evio Pawniard. A 10% chance to beat Magnemite 1v1. Foongus can 2HKO with Clear Smog, but will be likely to live two doses of Psychic even after the second hit loses the +1. Stunky loses 60% of the time. Likewise, Fletchling loses 40% of the time (Acrobatics is not insta-kill). Cutiefly is very resilient to other priority. It shrugs off Mach/Sucker Punch, and there are no STAB Bullet Punchers. Taillow's Guts Quick Attack does a third. Porygon can threaten it with a T-Wave, but unless it has backup, Cutiefly will just set-up fodder on it. Munchlax does not care and will pound its face in.

LO +1 Cutiefly will OHKO non-evio Pawn, both sets are not popular. LO Cutie gets nothing else of note.

Seeing as how Cutiefly's biggest banes are Steel and bulky Normal, a strong physical Fighting mon is a good complement. I'm looking at Timburr and Riolu. Even in match-ups that it does not completely win, Timburr can assist in knocking off the Eviolites that troll Cutiefly out of getting clean OHKOs. Diglett has also always been a fan favorite. Cutiefly appreciates hazard support, but is more vulnerable to it than it benefits from it, so it would not mind a pyrrhic Defog.

To summarize, these are just my notes on Cutiefly's offensive potential. I cannot ascertain how it compares to other prime sweepers in terms of OP-ness.