>>34749838>>34749319Gen5, no Hidden Abilities released yet, some gen6+ changes like new Defog and Pelipper/Torkoal having Drizzle+Drought, Gen7 learnpools (IE. Flygon learns Dragon Dance), Gen5 movepools (Flygon cannot learn Boomburst), certain items aren't working right now, no team preview, no fairy type but Outrage was kept at 90 BP and has successfully kept physical dragons manageable, no Pokemon not found in Emerald/Fire Red/BW1, no Rotom.
Current tiers weren't usage based but prediction based since it was going to take time until everything was implemented and didn't want ridiculous things to end up in a lower tier but soon it'll be usage based.
Does that somewhat fit your bill OP? Other than that I can't find anything that bans legendaries.