I'm curious what the major differences are between these two programs and why there is such a massive price difference.

I have been using Artrage for a long long time and love it. But I see Painter 2019 is in a Humble Bundle along with some other programs for $25. Wondering if it has any features or differences that would make it worth the extra expense? What does each do better or worse than the other?

Also I'm currently using AR5.