Bach, I affirm, is the foundation which all composers can be based off of. Not in terms of musicality
*big loud buzzer going NNNNNNNNNNHHHHHHHH!*
I think a lot of pianists tend to judge Bach by the fact that he didn't write for the emotive or percussive capability of the piano, and he didn't write for pedals or that level of resonance. That doesn't mean that his music can't be even more enjoyable on piano than it is on harpsichord; it just means that Bach didn't write for piano, and the art of pianism didn't really mature until the first half of the 19th century, thanks to better pianos and Chopin, etc. Beethoven habitually destroyed the pianos he wrote for, and the development of better instruments practically coincided with Beethoven's death (much like the earliest pianos were developed at the tag end of Bach's life).
But don't make the mistake of thinking that because Bach's keyboard music isn't pianistic, that Bach is not the foundation which all composers can be based off of, in terms of musicality (whatever that means, exactly...I have a feeling it's close enough). The concept of functional harmony, tonality, began to form in the Renaissance, and there were some composers of that age that were definitely talented, perhaps culminating with Palestrina. But Bach is nothing if not the foundation of functional harmony as we know it, in all its simplicity, and also with as much complexity as any composer since, probably up until bebop jazz. Bach never wrote a theory treatise, but he's inspired thousands, more than any other composer by far. Behind any great composer since his time, you usually don't have to look hard to find a reverence for JS Bach above all others. Bach was old-fashioned for his time, but even before Mendelssohn revived the St. Matthew Passion (and revived a popular interest in Bach), the elite, composers like Mozart and Beethoven, knew of JS Bach and revered him above all other composers.
That too. Bach is good for technique in the sense that his music will teach you independence of your fingers. He'll teach you how to be gracefully melodic without depending on the damper pedal. If you have problems with trills, then play around with Bach's ornaments - there are a bunch of different kinds, and he's not scared to put them in the left hand, even when the left hand also has another voice. If you can do those gracefully, then romantic trills should be no problem. I could go on. Obviously pianistic composers are important for developing piano technique, but pianistic composers <3 Bach.