Worth noting that the answer isn't quite as straightforward as simply replacing teeth with baleen, because we have fossils of whales that appear to have had both teeth and baleen

https://www.sciencedaily.com/releases/2021/05/210524091939.htm

Although other whale fossils that may be in the line seem to have had neither teeth nor baleen

https://evolution.berkeley.edu/evo-news/whales-lose-teeth-gain-baleen/

No surprise that something as weird as baleen is a bit mysterious