U do realise that Lando is immune to Charge Beam right? Not to mention that running Charge Beam means forgoing literally any of it's better options for a move which is pretty worthless in the great scheme of things. Also, BL is not a tier which is decided based on viability, but rather it's usage (and usage≠viability) and you can use 'mons from lower tiers in OU. Due to the fact that it's usage is pretty well spread across it's mega and non-mega formes relative to, say, Charizard or Garchomp or... most megas really, the usage on neither of it's base or mega form meets the OU cutoff. As an example of general consensus (keyword here is "general" as viability is subjective), it's current placement in the
OU viability rankings (with it recently having had the requirements for attaining all of it's ranks made stricter) it is currently ranked in A- whereas it's base form is ranked two subranks below in B (for it's LO set and to a lesser extent it's Sash set--Specs is still inviable no matter how much you say to use it over it's mega). You wouldn't bring it in against something it can't kill because it functions as a
revenge killer (i.e it is brought in when it is guaranteed to score a kill v.s. what it's in agianst). If I didn't use something just because it was frail then a lot of my teams would be immensely bad considering that I would need to replace things like Weavile with suboptimal choices, and the logic that you are using for why you wouldn't use your mega slot on it can be easily applied to Mega Lopunny and Mega Medicham, who are both extremely defining forces in the metagame. And it's not even like it has a hard time mega evolving versus stuff; it's high pre-mega speed means that it can MEvo versus a large portion of the meta and it's offensive firepower combined with it's offensive typing and coverage means that it forces a lot of common Pokémon out or outright KOs them while still outpacing them (including but not limited to Tyranitar (offensive variants get OHKOed by Focus Blast whereas the rare defensive variants die after rocks unless they carry Chople), Keldeo, Terrakion, Heatran (the most common variant (mono-attacking w/ max HP/Spe timid or 144 HP / 112 SpA / 252 Spe timid) can't damage it through Trace and gets chunked by Focus Blast; offensive gets outpaced and OHKOed after SR or, in the case of Scarf, gets mega'd on when locked into it's Fire-type STAB) and BoltBeam (T-punch+Ice Punch) MMedicham if given a free switch (OHKOed by Shadow Ball or chunked by Psychic (the latter KOs 87.5% of the time after SR+1 spike (if ur using MAla chances are ur using it alongside Spikes (which is coincidentally v. good in the current meta) so this isn't an unrealistic goal))). Once again, sand is everywhere so using Alakazam to RK Excadrill isn't an uncommon occurrence and it pretty consistently takes on Heatran (who is really common) specifically because of it putting this good ability to common use. While some of the scenarios (namely Natural Cure and Hydration) are less common than others, the undisputable fact is that it is still very regularly putting it to regular use against one of the most common and splashable Pokémon in the game as well as versus one of the most dangerous sweepers for offensively-inclined teams to be pitted against which is used in one of the most common builds atm.