Yes, Honda kinda gave up a little after the MC18.

Look at the 88. It was obviously right as the 89 went the other way on a lot of things. The 21 and then the 28 both mimic the 88 in many design areas, only with a softer edge.

I think that the 89 MC18 was Honda's usual trick of not refining, but just going the whole hog and making something new. Then they subtely reverted back to the previous years design.