I don't really see anything wrong with the pixel tech, specifically.
It sounds more like you're trying to improve your fundamental drawing/rendering skills. Whether oil paints or pixels, it's all the same principles.
I separate your character designs from the means you use to color them. Your pixelling is fine. Though your designs I do find bland. Symmetrical T pose?
But, since you're focused on PA, I have a suggestion - remove the design factor, use a few of Arachne's outlines.
See if you like any (don't miss that there are 3 pages, not just the one).
Grab a small one, color it, and report back here when it's ready to show.
One more thing, consider making your own palette. One that best serves the task at hand.