During Japan's Sengoku period is it known what proportion of the Daimyo were descended from earlier imperial bureaucrats or land administrators that had taken over power locally? Or were the Daimyo composed entirely of new upstart families after the collapse of central authority?

Pretty much all the families at least claim descent from a prominent family, and the claims are often hard to disprove or verify, so the first part of the question is either almost everyone or not answerable.

The second half though, while I'm not aware anyone did an actual tally and came up with a ratio, a lot of prominent clans came from at least Shugo-class families during the height of the Muromachi, including but not limited to: Shimazu, Ōtomo, Ōuchi, Hosokawa, Rokkaku, Imagawa, Takeda, and Satake.