I think that some of the people here really don't get how Mega Beedrill works effectively and don't have that much experience facing it. For example,
Pagoose (not picking on you, just trying to illustrate a point). Bug and Poison STABs are actually pretty damn scary for many mons in the tier, and with Drill Run to back them up, not many Pokemon wall Mega Beedrill. First of all, what you're saying is heavily flawed. When running Drill Run, the only mons on your list that can actually deal with Mega Beedrill are Gliscor, Gengar, Landorus-I, Landorus-T, Skarmory, and Scizor. Ferrothorn needs an enormous amount of defensive investment (which means it can't really beat Greninja) to switch into U-turn with any degree of consistency, and even then it never appreciates it. In general, it's a pain in the ass for offensive and bulky offensive teams, aka the dominant ORAS playstyle by a longshot, to switch into, as Landorus-T is really the only thing and Scarf variants can be worn out rather fast with U-turn doing like 35ish iirc (don't quote me on this it's anecdotal) plus cannot really go for U-turn due to Protect scouting that. Besides that, so much of the team is threatened by the sheer power and threat of Adapatability U-turn and Poison Jab. With such a powerful U-turn, it's really hard to punish it even with your counters because it can hit your mon for some damage and pivot right out to something that shits on that. There are very few situations where Beedrill's counters actually have some ability to take advantage of it. It is a huge offensive threat that is so good at retaining momentum for its team, especially with proper VoltTurn teammates.