Recommending Beedrill be moved
A -> A-/B+.
Beedrill is an interesting mon because so many things about it scream that it should be good. A smartly designed mega form in ORAS gave it ludicrously needed viability, allowing the Gen 1 trashmon to become a lightning fast and hard hitting harasser.
However, viability rankings are for a snapshot of a metagame, not what it may be in the future or has been in the past. And in this current metagame, I think that Mega Beedrill is not an A rank pokemon.
I base this argument a few tenants. First is the topic of the last few pages - opportunity cost. Simply put, I think there are better megas, Aero being the main one of these, and using Beedrill means you can't use him. This is an argument that's been done to death so no more elaboration is really necessary.
Second, a few of Beedrill's weaknesses are amplified by the current metagame. The following are factors prominent in ORAS UU today that hurt Beedrill: weakness to SR, huge amount of scald users, reliance on protect and incredibly low physical defense.
The weakness to SR is a big one, because in UU there are not a ton of reliable defog users. While mons like Empoleon do exist, they are fully prepared for in the current climate, fighting spam being what it is. Other options, like Crobat, are also weak to rocks themselves, which means the team will be increasingly weak to rocks.
Second, scald spam is everywhere. Simply put, you are not going to find a team these days without a scald user. Switching in or tanking a hit with Beedrill is madness when a burn effectively ends his entire game.
The reliance on protect is no good, because UU has many setup sweepers. The Beedrill user can predict a setup move and attack, but this is a bad situation to be in from the get-go.
Finally, having heinous physical defense in a tier where all of the best priority users use physical priority is horrible. Simply put, that massive speed becomes worthless in the face of any sort of priority, most of which can OHKO Beedrill, or certainly will after rocks.
Finally, the last thing I look at is his matchup against other top tier mons. Obviously Aero beats him all the time, Suicune walls him and wrecks with scald, even Mence is commonly scarf or DD and cannot be OHKOd. Not a favorable matchup against the S tier mons, and he fares little better against many common sets of the A+ and A rank mons.
Still, Beedrill can be a difficult mon to prepare for and a great momentum gainer and cleaner, but simply put I think that he is not one of the metagame defining choices a team can have.