Either make it so we can change the monster in Step-up Quests, or stop with the Dimensional Mutations.
With my equipment level and skill, I can somehow manage to defeat a ★9 solo, but, but beating a ★9 (Dimensional Mutation) solo within the time limit is just way too impossible. Rathalos (Dimensional Mutation) attacks far too frequently, and even if I attack without making a single mistake, 75% is the best I can do.
It might sound harsh, but if you’re no match for a 9-star Riftborne Rathalos, you’ll hardly be able to defeat anything even if you unlock 10-stars.
It serves as a very fitting stepping stone, so hone your gear and skills until you can take it down.
The monster’s moves are pretty different between regular 9★ and Riftborne 9★, so it’s a good idea to practice on Riftborne 8★. If you can beat it with no damage in under 30 seconds, I think you should be able to do it.
By the way, if you’re barely clearing regular 9★, it might also be worth reconsidering your damage skills.
I tried it and was able to beat it just fine with the pineapple gunlance, so I recommend using it if you have it.