Something like nerfing dps would be a good start. They should play a role in slowing/whittling down percies/bricks to make up for othuums/harbs being inferior, but not utterly annihilating them. Nerfing percies/bricks and then buffing snipers was a hard double nerf to the percy/brick vs sniper matchup. Seraphim mobile shields just further magnify this issue.
Maybe something like removing the sniper's ability to shoot while moving (or just decreasing its accuracy when its on the move) without touching its dps could also work, since it will still deal a lot of damage but atleast allow units to catch up to them.