It's kind of frustrating that 90s Trek actually gave an in-universe description for the ridgeless Klingons, because it really should have just been a case of "the aliens are the same, but this is how they're portrayed now". Like, my head-canon is that the TOS Enterprise looks just like the one in SNW; they just didn't have the budget/technology to accurately show it in the 60s. But now, there gets to be a plot hole of why Kor has ridges now, but won't 5 years later in "Errand of Mercy", and then will again by the late 24th century in DS9.