The flip side is you do run the risk of angering your HOF wen you draft his replacement; both Rogers and Love had to deal with that on some level. I've been critical about Loomis' transition.
Brees was all-in on Mahomes. According to Loomis and Payton, Brees was the one who told them to draft a QB after the 2016 season because he was starting to seriously consider retirement. Loomis said Brees not only knew about their interest in Mahomes, but was excited to have him on the team.
Just look at how Brees handled the end of his career in the playoff loss. Tears in his eyes, but he clearly tells Winston "this is your team now". Brees has always wanted his successor to be successful.