>people trying to classify mega evolutions as formes or evolutions
They're neither, of course. Formes aren't permanent, keep their shape outside of battle so long as the conditions required for the form are continually met, and keep the mon's species, but evolutions exist outside of battle, are permanent, and change the species.
Mega evolutions only last inside of battle, aren't permanent, and don't change the species excepting the "mega" in front of the name. I personally wouldn't consider these megas new mons because the majority of the megas just add a few new features or tweaks (color schemes, flames, spikes, fluffier hair, wing-like appendages), but they also aren't forms, as they are significantly "upgraded" rather than just "different."
But c'mon, you can't really claim Mega Kangaskhan is a new mon; her kid just came out of its pouch.