Absolutely, those are some really great points! Currently, most stages only has one solution, it ended up being a "rinse and repeat until you find the right solution" type of game. Once you know the trick it becomes really easy, I think this also essentially eliminate the "skill" element in my game that many great platformer has.
The fact that I know all the solutions to clear the stages has made me underestimated how hard the game is. That is definitely something I need to keep in mind next time while developing.
I think I can improve this by making levels with multiple solutions and perhaps adding some shortcuts that only can be done via manipulation of Speeding Up (for people who wanted the challenge and hopefully player will feel satisfied as well when they find a shortcut by themself). I also need to find ways to make it more obvious when to speed up/slow down, but that is something really hard to balance IMO. If it is too obvious, it will reduce the difficulty, and if it is not obvious, it can becomes very frustrating. Lot of things to consider, making a platformer is so much harder than I anticipated.
Thank you for your thought-provoking feedback!