I've been fiddling with the default brushes in 4.2.6 to try to find some painterly ones, but a lot of them seem to look kinda funny when I use them.

Example: https://i.imgur.com/qmLP3UE.png

The top ones are blurry, the bottom one is just kind of jagged and pixelated; the streaks through it don't look right at all. I've tried different brushes from different bundles and always seem to run into a few that do something like these examples and just "don't look right" in ways that aren't always easy to explain, so I'm hoping these examples will suffice.

Are these brushes really just supposed to look like that? I would expect them to look more like the little sample stroke in the icon for said brush preset, but they look like a mess.

Thanks in advance.

What size is your canvas? It looks way too small.

My canvas probably is on the small side, 300x400, but I'm looking at 100% zoom—isn't that more important?

That is not "probably on the small size". That is too small to do anything but pixel art. Certainly nothing painterly. Add a zero to either dimension.