Beedrill doesn’t exist in a vacuum I.e the mons you mentioned (ghostceus and Etern) are fairly easy to tech for esp considering you’re typically pairing it with another phys attacker like chomp or greninja. Mosa also lacks stab poison moves and has to go outa its way to run d ascent. M zam part is fair tho.I think Beedrill's biggest issue is that you cannot hit everything and the stuff you don't hit are really hard to bypass
Mega pert only takes mildly more percent then smth like mega audino and the defensive dragon types are fairly mid rn (mostly because of getting blown past by offensive dragons, which pert doesn’t entirely.) spdef sets job isn’t really to wall m zam flutter more it is to have a backbone vs Etern and miraidon.This never has the bulk it needs to check anything. As a water immune to electric it sounds cool but stuff like Chomp just blow past with STAB so the only niche is beating Fire/Elec Hooh which you can do with a dragon! SpD sets get blown away by zam flutter etc
It retaliates with like, knock off at best (scald isn’t too consistent). This is also taking the arc slot for smth that can be done pretty much better by the above mega pert.Waterceus has a very clear niche which is the fat water type that does not immediately fold to Electro Drift
Also
remove regen imo, all it maybe does is some speed control (which faces immense competition from well, every other speed control). Prim sea is still decent cause of the greater phys bulk over registeel without taking up arc slot.
add bounce it’s not bad better then prank/regen prolly.