nah there's more to it. Every subgenre of rap, from hits-driven to alternative, conscious to gangsta has its cliches and gimmicks. And they're all equally the same in shyttiness and shallowness.
yeah but changing your style in itself does not automatically = gimmick
if its an organic style change, and it works, then word up.
but if its clearly a forced style change to stay relevant or cater to whats hot, then yeah, its no good.
there are plenty of rappers who stay in their lane stylistically, because its what they like best/are most comfortable with, and feel most inspired by. i wouldnt stay staying in your lane is a gimmick, especially if you continue to release quality music.
it all comes down to intent
i dont know kendricks intent with the style change in this album, but it also doesnt seem like a huge style shift that i would classify as a gimmick.
if anything it seems like a continuation of what he's been doing
at its core, its still kendrick bringing the same content he has been