>>41708880>ClefableThe only time a Pokemon's type is changed baseline is when a new type is added. Magnemite/Magneton got Steel added, but nothing became Steel; likewise, nothing became Dark or had Dark added to their type combination. For Fairy, type was replaced ONLY if it was Normal; everything else had Fairy added a la Magnemite. You could bring up regional variants, but those are essentially different Pokemon entirely, especially now that we know regional evolutions will be a thing.
>PelipperDrizzle + STAB Hurricane. Rain continues to be a busted weather; more at 11.
>Serperioris carried entirely by Contrary Leaf Storm, and even that's not enough considering it has no moves and has a measly 75 SpAtk.
>BlazikenNot a shitmon.
>ScolipedeNot a shitmon, especially not with Speed Boost and access to Baton Pass.
>Tangela and MurkrowThey got evolutions; Honchkrow's isn't even good, while Tangrowth's didn't become good until it got Regenerator. You're also overlooking that a large number of the Pokemon that got Mega Evolutions are either part of a 3-stage line, or have base stats high enough that they can't realistically receive an evolution.