you use the same brush all the time and id be down with that but you gotta mess with some of the brushes my man.
turn that hardness up, the brushes you use seem to have too much anti aliasing which isn't bad but with some items like fur and well solid objects like horns.
its mostly your highlighting that are consistently blurry. it actually makes it hard to tell where the brow hairs start and end. its also pretty messy (brows, lips, teeth etc.)
i get that its a first wip but these seem to happen a lot with your heads.
20 minutes? yeah, definitely spend some more time on heads, you will see a huge improvement the more time you take on them. not only this but the more time you spend drawing a head, the more time you're learning and gradually getting better.