The BPs are voted in by the EOS holders. So if the BPs are not behaving appropriately then the EOS community simply votes them out and a new BP is voted in.
Another question from me: Is the voting power proportional to coin held?
Yes. 1 coin = 1 vote There is a couple “sister chains” Telos and Worbli that are developing a slightly different voting model that are expected to prevent whale manipulation.