In some cases, yes. In other cases, no. Some of the unevolved Pokémon that got mega evolutions in Gen 6 were already viable enough competitively. Heracross, for example, already had very good stats. Its mega evolution just makes it more viable in competitive play.
Now, as for Sableye and Mawile, you could make the argument that they would have been better off just getting regular evolutions in order to increase their stats...and then to give them mega forms. Hell, Mega Mawile looks like it could just be a regular evolution for Mawile. However, it could go either way really.
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My Friend Safari type is Flying, with Fearow and Swanna.