The game certainly had better courses than the ones chosen, and none of the tracks you mentioned were particularely good. Mario circuit and luigi circuit? Meh.
Dry dry ruins was shit as well, although this is again partly "fucking heavy bikes have an even bigger advantage because of this track being so bumpy" thing. (same is partly the case for the 3 other ones already in the game, and probably won't be a problem in mk7)
So yeah it's also bullet bike bias here. The amount you jump and bounce with these, plus the amount you can get pushed around by people who lag into you (which is always the case with bumping in mkw)... dumb.
Good/decent courses: Toad factory, daisy circuit, moonview highway, bowser castle I guess. Bowser castle still not that high on my list considering it is a bowser castle though, they've always been good to me.

^So you're right, mkw had a horrible stagelist. Doesn't change that the ones picked were all among the ones I hated the most when getting picked online, and they were all weirdly popular. MG's weird popularity was like... YF in mkds.
I do think some of them might work better in an actual better game though, but the ones chosen are all just not that good, and I see no hope for MG in any mk. Plus there were a decent amount of great retro courses in mkw so clearly it was possible to make good courses for the worst game in the series

(why was DKJP and BC64 wasted on that game?

)