Personally, I see this more as a case of expanding options for artists and game designers. Yes, sure, some artists will make 32x32 tiles while others do 48x48, but why shouldn't they have that option? For that matter, why shouldn't they have the option of making 16x16 tiles if they want? And why shouldn't game designers have the option of using different tile sizes? Let's face it, thanks to the end of hidden classes, if RPG Maker MV doesn't let you change tile sizes by default, there will be a script to let you do so.
And of course, your statement assumes that the overall pool of artists would stay the same. For all we know, it might well expand because there's options for people who don't want to be forced into making 32x32 tiles. And if that happens, the range of available resources per tile size will increase, or at least not decrease as much.
I agree, of course, that being locked to 48x48 tiles wouldn't be so good. But then, being locked to 32x32, or even 16x16 tiles isn't all that good either, if you ask me. It's all about options. And allowing for new tile sizes is by definition expanding options.