I tried Iray, and actually the result for my test model was quite ok there (and not ok in Arnold). The reason I exported everything back to Maya and tried Arnold is that I can configure the render scene there (light sources, for example), which I cannot do in Substance Painter. Currently I am using Maya; I haven't used…
It's a well known limitation of ray traced renderers vs game style rasterizing like the one in Substanse painter. Ray tracing just doesn't work together with normal maps same way. You will always see those artifacts in any offline ray traced render nowadays. Nothing to do about it. Even in games "contact shadows" which are…