But Mega Blaziken can use Swords Dance, and Mega Evolution does not waste the turn. So Mega Blaziken can use Swords Dance and about as powerful than Blaziken using Swords Dance.
48.03 - 56.69% vs 50.39 - 59.58%
The first percentage is how much a Mega Blaziken would do with max Attack EVs, Adamant, and Return if it was a Normal type vs an Arceus.
The second percentage is how much a Blaziken would do with max Attack EVs, Adamant, Life Orb, and Return if it was a Normal type vs an Arceus.
Ignore the fact that it is a 2HKO on Blaziken since I did make it Normal typed and having Return, and the Arceus had an unrealistic 0 HP EVs in both situations anyways.
So this says that Blaziken with Life Orb is only somewhat more powerful than Mega Blaziken. And the price to pay with this is 10% Life Orb recoil, which stacks with the fact that its moves are so recoil based (High Jump Kick and Flare Blitz). We also have to take into account that it cannot outspeed the Scarfed Pokemon of base 90 Speed (of which we see a decent amount of) without getting two Protects in. Also, Mega Blaziken is slightly more bulky, with 10 more base defenses.
I think the benefits of Mega Blaziken as such outweight the con of a dealing 2% less damage. The only reason not to use it would be because you have another Mega on your team you would want more, as might very well be the case.