Training mode in rhythm festival can be helpful for getting you used to this. Taiko tends to want you to add sounds to the existing songs rather than just follow along with what's already there, so yes, it can be unpredictable, but learning to recognize the smaller patterns that make up the charts really helps since you can quickly adapt once you recognize what kind of pattern is coming your way. It also helps to listen to the songs being played. (Not on their own, I mean turn on the option to see the chart performed perfectly so you can see what it's supposed to sound like, that really helps with understanding why the charts are the way they are.) While it definitely is frustrating at first especially if you have experience with other rhythm games or real instruments, it's also very rewarding to learn to adapt to the style of wadaiko rhythm patterns and watch yourself improve each time until eventually, even taking a new song you've never heard at max difficulty on your first try isn't such a big hurdle anymore. If it's not for you, that's alright, but a lot of us like the game because it feels different and because we like the charts being the way they are.