Pretty sure it was said in an interview that the data structure was revamped due to the incompatibility, not vice versa. Plus there's been a (admittedly minor) data structure revamp in every generation since and they've still maintained compatibility.
And how many of those things are competitive? 0 of them are OU and Heracross alone is borderline.
And Scizor's the only bug type you ever see that actually uses bug moves. So just don't have it out against Scizor.
This and U-Turn are the only bug moves you actually have to worry about coming out unexpectedly, but that doesn't make a 4x bug weakness much of a problem at all. Pokemon with 4x weaknesses to a lot more common and versatile types than bug see competitive play.
Smogon's tiering doesn't count outside their own metagame, and I've seen plenty of Volcanora and Heracross use in GBU, both of which often have Megahorn/Bug Buzz because it's good coverage. U-Turn makes it on a lot of sets, just because of its use in scouting.
Plus Scizor is pretty centralizing still. 4x weaknesses aren't a death warrant, but bug is a pretty important attacking type to have to watch out for when it's STAB for two heavy hitters, both physical and special.