Almost no commercial or PD texts have soft hyphens of about 6,500 ebooks I've checked. I removed them from one.
I do read on the Sage mostly, but I read for years on PW1, then DXG, then PW3 and still check ebooks on mobi and azw3 on the Kindle Keyboard gen3 (maybe 1st decent 800 x 600 kindle when they retro-added azw3). The DXG was a bad buy, but I'd passed on the PW1

Then I got an original H20. I really can't see the value of adding soft hyphens.
I don't see a problem on the Sony PRS350, T2, tiny Y-Ben 4.7″, or various Android apps.