It’s really only more secure in the sense that in general more complicated programs have more things that can go wrong with them. Either bugs, or just user error.
That is a valid concern, and most people don’t need or use any of sudo’s extra features, so it’s completely reasonable to switch to doas because of that, but it’s not like there’s some glaring security flaw in sudo that most people really need to worry about. Especially if they’re not doing weird things in the config, which would mostly be the same people who could easily switch to doas anyway.