Just a small note that Levitate/Air Balloon/Magnet Rise/Telekinesis Targeted/Flying types don’t benefit from Terrain, so your point on Ray benefitting from Psychic Terrain does not apply.
It's not a direct benefit. Psychic Surge (and Dazzling) discourage people from running Fakespeed Refrigerate/Pixilate sets in general. These are two of Ray's biggest offensive checks/counters, so even if Ray got zero direct benefit from the terrain, it still enjoyed its presence for weakening and removing some of its major roadblocks from the meta.
Compare to ORAS, where Ray survived the GKR ban partly because it was forced to run King's Shield or switch out to avoid getting giga-wrecked every time Diancie/Kyurem/-ate lures got in on it.