People asked for a Dragon Quest characters for years. It just wasn't noticed in the West because most people were too busy shouting "WALUIGI/ISAAC/GENO/BANJOKAZOOIE" etc, so the demand got drowned out.
Hell, even TV Tropes pointed out how much the West and East sides of the fanbase are disconnected from each other. And the worldwide fan polls have samplings that vary wildly to the point that the demand for some companies isn't taken for account at all, it's practically like Family Feud.
Sak wanted to ask for Hero/Luminary himself, if that didn't work, he would have taken the suggestion of Slime as a back-up plan, so DQ11 on Switch was just convenient timing. Besides, Erdrick's games were not even advertised in the flipping slightest until a few months after release. Bayonetta is pretty much just a case of doing Kamiya a favor.
So what if the character you want promotes something? That'll make them get love they wouldn't have gotten otherwise, especially given the unwarranted bias detractors tend to have against their potential inclusion (too violent/too sexy/only AAA names are allowed/literally who), as Smash has really strong brand power. I mean, Shantae has already promoted Blaster Master and Studio Trigger, so if anything it's too late to assume she wouldn't shill anything.