Dear lords, that’s the most negative rant about Mega Evolution I’ve ever seen in Smogon Forums!
That said, I agree how much of net loss Mega Evolution caused in the long run; it doesn’t help that GF intended it to be one-timer either, making the concept feels more and more insincere, and I’ve seen too little fangames implementing them without significantly rebalancing them, either.
I know
Samtendo09 is famously more critical about fangames than the average Internet person, but man, I agree with this individual. "Everyone is Here" is a bit less meaningful if the lesser critters of the kitchen sink are as unviable as ever.
When the official Megas are implemented, you can bet your butt they won't receive any change except one or two Abilities and typings. M-Beedrill is still as frail as ever, for example.
Basically,
if the base form doesn't get a stat buff, neither does the Mega, which makes sense I guess, but
this causes some Megas to be favored over others.
Case in point,
Mega Audino, one of the more controversial Megas thanks to a combination of "overshadowed by other Megas" and "why didn't it get a proper evolution?" It is notoriously weak-hitting without Calm Mind (especially by Mega standards) with an Ability that's useless in Singles, where walls are more performant than in Doubles. It's little surprise it's one of the worst competitive Megas, hanging in NU with two Ice-type wallbreakers as the only competition for the Mega slot. It could have been better. Healer is a fitting Ability flavor-wise, but most can agree it's just not good.
In
Radical Red, it got one buff, namely the Mega getting the Regenerator Ability. While it's a great buff for a defensive Pokémon, it still suffers from mediocre offenses: still slow, still can't hit that hard.
Then there's
Inclement Emerald, which changes Audino's and Mega Audino's stats. I didn't play this game so I can't tell you how good it is, but the Mega gained 40 points in Special Attack as well as Fairy Aura, so it's more offensively potent, but the game also has competition for offensive Fairy-type Megas such as Altaria Gardevoir, Mawile, and even Milotic. Audino has its uniques strengths, but I'm not sure if that's enough.
And this is the issue with balancing Mega Evolution: Are the stats good enough? Is the transformation worth giving up an item slot? Should I pick someone else with this option? You might think more choices is better, but in practice, less performant options are less likely to be picked, so diversity isn't that much of an upside.
Which is why XY NU and SM NU are great metagames: in the former, Audino is the only Mega option; in the latter, Audino only competes with two others, and it plays very differently from either.