Why is one screw in V-brake a lot tighter?
I suspect the brake arm with the tighter screw needs a good cleaning of its internals. Try spraying some penetrating fluid like wd-40 in between the brake arm and the pivot and see if that helps at all. If cleaning (thoroughly, when taken apart) doesn't solve the issue I can think of a few alternative reasons your brake arm might not be properly moving:


The cable and housing can pull the brake arms to one side (adjust cable routing)
(suggested by @Argenti Apparatus in the comments)
Mount bolt too tight on 1 side
Spring incorrectly installed (unlikely)
one of the o-rings seen in the diagram below is incorrectly installed/seated


Are you sure your rim is properly centered in between the two brake arms? If not your wheel might need dishing or it might need to be centered on it's axle.