Sometimes, even main villains aren't immune to feeling clichéd or disposable, and in The Defenders, those villains were two of the five leaders of the Hand, Murakami and Sowande.
While these two were integral to the Hand's plans behind the scenes, you don't actually get to see them do a whole lot of anything. (Besides get defeated by the heroes, of course.) Plus, unlike Madame Gao and Bakuto, these two don't appear outside of The Defenders, which doesn't exactly help as far as character building goes.
With Sowande dead and Murakami presumably the same after doing very little, these two are the bottom of the barrel when it comes to main villains.