I know this is a fairly old thread but many artists ask this exact same question and are still trying to figure out how to get sharp renders out of Maya/Arnold. Its a tedious process - someone needs to write a script for this.
I worked on this for a couple of hours and have figured out a workflow that works for me on getting sharp(er) renders. Here is a megascan cracked concrete render. The default settings in Maya produce blurry renders. Turn off all texture filters for each texture. If you are using displacement make sure that use at least 6 iterations on a high poly mesh to maximize detail, this of course depends on how far away your camera is to the subject. In render settings switch to closest or blackman harris - maybe setting to 1 on gaussian will work to. I wonder if Maya sets up textures thinking that everyone is going to animate and do single frame stills.
