A simple solution - no fine structure nor width variations, only some zigzag, can be achieved with an effect. It's applied after the curve has been drawn. This is from Illustrator:
But Affinity Designer hasn't it.
If you use complex realistically texturized lines as vectors, it slows down common drawing programs. In practice you cannot have the effect as you draw, you must add it afterwards. That's obviously not a good thing because you would draw differently if the stroke is the final one - no matter is it done by free hand or more technical curves.
For ex. Inkscape allows you to draw in the fly so that the stroke pattern is taken from the clipboard. As well, after you have drawn a shape, you can place pattern along path. That can be a path effect, or a more flexible extension. Inkscape in addition has numerous filters which can reformat strokes. Here's an example of path effect:
As said, very soon as you insert more curves Inkscape becomes slow preventing effectively rapid drawing if you use something finer than simple strokes. It's still possible that the performance is acceptable, if your pattern is simple enough. One centimeter of the stroke surely is non-realistic, but as a whole, it can be acceptable An example:
Here's an artificial bitmap stroke and the same as traced to BW in Inkscape. When the traced version was copied to clipboard and new curves were drawn with "take the stroke pattern from clipboard" the new stroke appeared well under half second after completing the stroke. So, it is a simple stroke until you release the mouse.
You must also do diverse trickery to prevent the pattern to be squeezed too much for short strokes, Generally you must have shorter versions and apply them afterwards for short strokes. Long strokes can be handled with splitting the curve here and there to avoid stretching the pattern too much. Here's an example of long curve. The pattern is from clipboard and the curve is splitted to four parts at nodes:
But the non-stable curve directions become easily without asking. Draw non-smoothed paths with a mouse.
Unfortunately I do not know how a draughtsman with ultra stable hands can especially program a high quality drawing tablet to insert direction variance (never needed additional instability) That variance should be in the software brush.
Affinity Designer's image brushes which really are repeated PNG images, are a crossing where the fence is lowest. The drawing performance can be tolerable, especially when you use low res images. The paths still stay editable. You also can change the brush afterwards globally or for selected paths. I don't see Affinity Designer's solution by any means an overkill. My opinion: it works very well. Illustrator also has the same in CC versions.
In bitmap graphics programs (GIMP, Photoshop, Affinity Photo) you can draw paths and stroke them with brushes to keep things still editable. Or you can draw directly as bitmaps without path editability. Paths in bitmap programs are auxiliary tools and their editing & combining possiblities are more rigid than in vector programs. I cannot recommend them ecxept if you draw directly the final curves as bitmaps and do not need heavy edits. Even better performance in that case is probably got by using 100 years older tools.
Theres still one way to make variance: Bitmap images can be distorted with numerous filters. They can have small feature noise as well as waveness in a larger scale and all randomized. Unfortunately they are not "in the fly", but post processings. Photoshop's smart filters can offer a possiblity to see the result also when wanted during the drawing work.
here's an example of 2 different filterings in Photoshop. They are random attempts, not especially tried to simulate something special.
In the left a ripple effect is applied, In the right theres more effort. The shape has got waves filtering to create bends, there's a slight amount of blurred noise added to the image, then tresholded to make the stroke grainy. Finally a little horizontally shifted copy is added to make the line widths in large scale non-uniform.
Remember: You can keep your vector images and goto Photoshop or other bitmap program for stroke effects. Finally everything is shown as bitmap, there are no vector screens nor newspapers.