Hello! I adore the artist crumb on Tumblr and they shared the brush they use for lineart a while ago. It seems to be one of the default brushes, but it behaves a bit differently? At least i can’t get it to work the same way in the video. When i make fast/short movements the lines…seperate? What can i change to make it more like theirs/ more suitable for lineart? heres the program and brush i have been using for my rick and morty comics, as well as how i draw them for those who have asked!... – @crumb-crumblet-s-crumbington on Tumblr
Hello @Rin3 and welcome to the forum 
v) Sketching-3 Leaky is one of the default brushes that is in the Krita_4_Default_Resources bundle. It seems to work fine for me.
It uses the Curve Engine (not the Pixel Engine) so making adjustments/changes to it would be unfamiliar to people (like me) who are more used to the majority of other brushes.
Can you post a screenshot showing what you mean by that?
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At high speed and small size, there is line separation because of how the Curve Engine constructs strokes.
It may be that in making a fast stroke you are also not pressing down on the drawing tablet.
At low pressure, the opacity of the brush is reduced to zero but that doesn’t seem to be a factor in producing separation of a painted stroke because even at high pressure there is separation.
All I can suggest is using a slow drawing speed because it seems to be how the Curve Engine works.
Someone else may come along who knows more about this.
It looks like of i press down REALLY hard it works better 
I havent changed the pressure curve(?) thing ever since i got this tablet, maybe adjusting it will help?
The pressure characteristic of that brush preset is that its opacity reaches maximum value with a pressure input of 50%.
So changing the pressure curve won’t make any difference with high pressures.
You can try it. You can try anything but I think it’s just the way that brush is.
It’s the only brush preset I know of that uses the Curve Engine so it can’t be easily compared with other Curve Engine brushes,
Aww shucks. Well, thank you for the info 