I find it very interesting how GF chose to give the Tapu's terrain moves as abilities. Terrain moves were relegated to only being useful in niche strategies last gen due to how counterproductive they were, i.e. every Pokemon on the field benefits from their effects, including the opponents.
Grass Terrain will heal your opponents and make them resistant to Earthquake (which for Tapu Bulu is really bad since he needs Earthquake to cover his Poison, Fire and Steel weaknesses, hopefully his SpA is decent so that he can use Earth Power), Misty Terrain will make your opponents immune to status and thus allow them to easily set up and Psychic Terrain will make your opponents not be affected by priority moves. Electric Terrain is the only move which the benefit to your opponent isn't a big deal since sleep immunity isn't all that, but that is the root of the problem, near every Pokemon you will face can take advantage of being under Terrain conditions without having to prep beforehand, unlike with weather which only Pokemon set up to benefit from it can.
Maybe the Tapus not having to waste a turn to set up terrain unlike other Pokemon could make it somewhat more useful, but I can only see this being something that can only really be taken advantage of in doubles rather than singles, which I guess is the point since VGC uses the doubles format.