Project Gutenberg's formatting of epub is based on text as they started in 1971 – 1972. It's easily automatically reformatted by Calibre on an epub to epub conversion. Then it's often better than Standard Ebooks. See also Global Grey.
https://www.globalgreyebooks.com/index.html
PDF is terrible except for print, or content that needs fixed layout like textbooks, illustrated children's books, graphic novels or comics.
ebookzy looks tiny and could easily be created from Gutenberg. So I downloaded "The 39 Steps". Other sites have far more of John Buchan's novels. It is from Project Gutenberg.
So ebookzy is pointless.
EDIT:
It's also a poor website as the categories miss titles they have and the covers are using stupid web page coding such than on my 4K 23" monitor I have to scale the page to 67% to avoid all the covers being cropped on the right.