So since it can technically not evolve and would be broken as all f*ck, is it safe to say she isn't allowed?
I don't think its capability to evolve is relevent. XY OU does not even have a dozen pokemon that avoid a 2HKO. Here, we have next to nothing. Some calcs (note that I did fix the special attack. I use Moonblast as a placeholder for Light of Ruin.
252+ SpA Choice Specs Floette Moonblast vs. 252 HP / 252 SpD Chansey: 147-174 (41.1 - 48.7%) -- guaranteed 3HKO after Leftovers recovery
252+ SpA Choice Specs Floette Moonblast vs. 252 HP / 252 SpD Chansey: 147-174 (41.1 - 48.7%) -- guaranteed 3HKO after Leftovers recovery
252+ SpA Choice Specs Floette Moonblast vs. 252 HP / 252 SpD Rhydon in Sand: 159-187 (75 - 88.2%) -- guaranteed 2HKO after Leftovers recovery
252+ SpA Choice Specs Floette Moonblast vs. 252 HP / 252 SpD Piloswine: 205-243 (99 - 117.3%) -- 93.8% chance to OHKO
252+ SpA Choice Specs Floette Moonblast vs. 252 HP / 252 SpD Sealeo: 187-222 (94.9 - 112.6%) -- 68.8% chance to OHKO
252+ SpA Choice Specs Floette Moonblast vs. 252 HP / 252 SpD Pignite: 214-253 (108.6 - 128.4%) -- guaranteed OHKO
252+ SpA Choice Specs Floette Moonblast vs. 252 HP / 252+ SpD Porygon2: 144-169 (75 - 88%) -- guaranteed 2HKO
252+ SpA Choice Specs Floette Moonblast vs. 252 HP / 252 SpD Rhydon in Sand: 159-187 (75 - 88.2%) -- guaranteed 2HKO after Leftovers recovery
252+ SpA Choice Specs Floette Moonblast vs. 252 HP / 252 SpD Piloswine: 205-243 (99 - 117.3%) -- 93.8% chance to OHKO
252+ SpA Choice Specs Floette Moonblast vs. 252 HP / 252 SpD Sealeo: 187-222 (94.9 - 112.6%) -- 68.8% chance to OHKO
252+ SpA Choice Specs Floette Moonblast vs. 252 HP / 252 SpD Pignite: 214-253 (108.6 - 128.4%) -- guaranteed OHKO
252+ SpA Choice Specs Floette Moonblast vs. 252 HP / 252+ SpD Porygon2: 144-169 (75 - 88%) -- guaranteed 2HKO
I think my argument for quickban holds (assuming it is allowed).