for hand painting i second the 3d coat recommendation. http://img05.deviantart.net/674c/i/2015/068/b/5/golem_bust___part_2___texturing_in_3dcoat_by_turpedo-d8l2e3b.jpg
are you smoothing the uvs in render or something? Also is that viewport texture display for arnold shaders new to 2018, or can you do that in 2017 too?