It's true that every run will rely heavily on RNG. But there are certainly optimizations that can be made to every run and decisions that players can make. It usually doesn't mean much but it can certainly mean the difference between an extra minute or two. Some examples in story mode:
In Bound of Music there's an extra animation for every note you hit. It's about .3 seconds long. So the optimal solution is to get one more note than your opponent and walk into them to prevent them from getting more.
In Sky Survivor and Shock Absorbers you can push your opponent into the obstacles.
Some players like to get capsules for the chance of getting a mushroom or spiny. The downside is if someone lands on a Kamek space and you have to sit through the capsule shuffle -- and then a koopa kid's use of the capsule.
Knowing the boards can help too. I've found myself spending extra time viewing the board when I come to a fork. Or instinctively choosing the short-loop when the long-loop would give me a VS space to end the game.
It's an RNG heavy game but you can strategise a bit.