I think if the painting were perfectly identical than it'd be just a reproduction and it should violate the photo's copyright, but even if such a thing were possible for a very skilled artist to pull off, I don't think that'd be something that happens very often. I'd guess that most artists would have a hard time not making changes.
We want artists to be protected from outright reproductions of their work, so that'd include minor low effort changes in photoshop made just to get around copyright. Artists should be free to create their own versions of existing works though. Copyright is supposed to encourage the creation of art after all.
OK. You should make it clearer that you're arguing for a weaker system of author's rights, not just making claims about the current system. I favor copyright reform but what you're suggesting would destroy the ability for artists to commercially exploit their work.
We want artists to be protected from outright reproductions of their work, so that'd include minor low effort changes in photoshop made just to get around copyright. Artists should be free to create their own versions of existing works though. Copyright is supposed to encourage the creation of art after all.