>>26822507IVs aren't the problem, hacked legendaries are. In my opinion the best solution would be to flat out ban all legendaries. Not because all of them are powerful, but because getting legit perfect legendaries is practically impossible, and thus hackers have a significant advantage over people who play legit.
Breeding is easy, especially if you have a good breeding stock. When you begin breeding for the first time it's going to take time, but once you get the ball rolling it just keeps getting quicker and easier. I know this because I started in XY with Friend Safari Mons with 2 IVs but now that I have like four boxes of competitive Mons I can breed pretty much whatever I want very quickly. Even going for 6 perfect IVs isn't as difficult as many people believe. Once again I speak from experience as I have a hexa Protean Greninja that I bred myself. Besides, I don't even have the "hexaperfect seven" which would make breeding even more convenient.
Also, banning all legendaries would remove the cancer that is Landorus-T and Thundurus.