For the beginner intermediate level, scales and arpeggios are enough for technical exercises. However I still view them like a vitamin supplement. They are important things that everyone needs to some degree, but they don't provide all the technique you need. There is still some types of technique that you need to get from actual music.
In terms of your curriculum. There is some odd things. Many of the Little preludes/fugues are actually harder than the inventions. Even though the inventions are considered easy, they are only really "easy" if you are talking to conservatory level pianists. Most learners will take 5-7 years to play even the easiest inventions.
Here is a simple and effective plan to boost technique:
- Go to the RCM Syllabus
https://rcmusic-kentico-cdn.s3.amazonaws.com/rcm/media/main/about%20us/rcm%20publishing/piano-syllabus-2022-edition.pdf- Start at level 3
- Pick 30-40 pieces for each level (more pieces is preferred the higher the level is). You don't have to do this all at the start
- Learn them.
Now you may say, "Those pieces are too easy for me." If so, then they will be great for improving your reading and playing fluency. I did a group beginning piano class in school after 10 years of piano lessons (for school credits), and still found something to learn from each piece. And while you won't learn as much from the easier pieces, they will also be much quicker to learn.
Why do people not practice this way?
- It is not often encouraged by teachers because parents want their kids to play impressive things and adults don't want to learn "rudimentary music"
- While it is fun, it doesn't have the immediate appeal of a big famous piece. But at grade 3 and above, there is a ton of quality music.
Why should you practice this way?
- It will boost your reading skills a lot. I know some people who were playing Chopin Etudes who would struggle to play bach minuets. And while this is an extreme example, It's good for an amateur player to be the opposite. Be able to sight read the simpler pieces so you can just sit down and play.
- There's far less friction and roadblocks in progression. If you see something new, it will rarely be difficult. If you see something difficult, it will rarely be new.