It seems the only Isekai I hear about these days (at least from friends and on this site) are ones where the characters have "video game skills", but reading up on the genre that's not the only theme, and many don't feature that. It's more or an overlap with LitRPG.

I'm going to specifically limit this to 'Skills' - any numeric value assigned to an ability, that is intrinsic instead of assessed. So people being assessed and graded doesn't count. Skills can increase, but not by grading (like going up belts at karate).

Also just assigning levels aren't what I'm after, so no "It's over 9000!" from Dragon Ball.

When did this aspect of Isekai start?