I put emphasis on splitting spacebar into thumb keys just because the large spacebar is so ubiquitous. -- There's practically no downside to splitting the large spacebar into 6x keys.

I think it's good if layout enthusiasts want to use as few as keys as each finds practical. -- I think a good keyboard will support layouts that bring the full functionality of the keyboards to within the hands on home row for two-handed typing (as well as support mouse + keyboard functionality).

But .. I think that the keyboard is physically better off with fewer keys is just fashion amongst enthusiasts.