When I use the palette knife it looks like the paint is filled with lots of lines everywhere. In real painting this is not what it looks like. The paint is smooth with no lines. And in the new 2019 version when I use the paint tube for some dumb reason they put a horizontal line right in the middle of the paint. Once again in reality there is no line in the paint. Why Corel does these things is beyond me.
I'm not sure what paint tube tool does in painter, but it would help if you've posted a couple screenshots of the issues you run into.
painter's palette knife (the one found in "sponges and palette knives" category, it might be different in the most recent painter version tho) is basically a flat brush, consisting of tiny parallel hair streaks that shoot out from a single point.
it wasn't designed to behave like a real palette knife that you'd use with oils or acrylics - artrage replicates that more closely to the real medium.