Bryan Fuller, the creator of Star Trek: Discovery, left the series in 2016 due to "creative differences," but fortunately he stayed long enough to get the lead actress he wanted on board. In an interview with the D-Con Chamber[via Screenrant] with Star Trek: Enterprise's Connor Trinneer and Dominic Keating, he said getting series star, Sonequa Martin-Green wasn't easy as CBS Studios didn't want to wait for her.
Martin-Green was still working on The Walking Dead, and Fuller told the studio to "push production" so they could have her for the lead of Discovery. He said the studios resisted and "I was fighting for Sonequa. They didn’t want to wait for Sonequa, and I was like, ‘Push the production. She’s great.’”
Some fans would disagree with the choice to play Captain Michael Burnham, and there were plenty of Star Trek fans who took issue with the way Martin-Green played the role. However, It's difficult to imagine anyone else as the mutineer turned captain.
Martin-Green didn't get to come aboard Discovery as a captain, and she was the only other Star Trek captain who didn't start out as one. Avery Brooks was the other, taking over Deep Space Nine when he was a commander on Star Trek: Deep Space Nine. At least he was in a position of leadership. It's an even heavier load to be a lead of a show when you're not in a position of leadership on the series.
Was everything always perfect? No, but Martin-Green really gave her all to that series, and there are plenty of fans who believe she was the best choice to play Burnham. Fuller pushed in the right direction, and because of that, Discovery lasted five seasons. That mgiht not have happened had the wrong person been cast as Michael Burnham.