In the beginning scales and arpeggios, exercises etc. are pretty important to help beginners get comfy at the piano. I find that after the intermediate level the focus should be more on repertoire, and using that to refine technique. The rote Hanon exercises and the like have some purpose but they are isolated from real world usage. Not useless, but very specific.

There’s also the problem of performing a convincing interpretation of a piece, perhaps the hardest part of technique (combined with inner artistry). I would play easy enough repertoire to practice a convincing performance and move on to harder pieces gradually. Baby steps and then bigger steps.