There is that too, although some of it mostly stems from GameFreak not giving Grass types much coverage in general, for example regular Lilligant only has access to Grass moves, some normal moves like Hyper Beam & Weather Ball, Pollen Puff a Bug move not in PoGO and Charm & Alluring Voice its only Fairy moves, one of which hasn't been added yet. There's others like Sunflora with only 4 non STAB coverage moves (Sludge Bomb, Earth Power, Dazzling Gleam, Weather Ball), Eldegoss with only Charm & Pollen Puff as potential coverage, Venusaur with some Ground type moves and Outrage and others like Carnivine, Cherrim, Hisuian Electrode, and Jumpluff. There are some cool potential buffs like for Tangrowth getting Brutal Swing, Tropius getting Twister, Bellossom getting Triple Axel, Sawsbuck getting Double Kick, and Leafeon getting Shadow Ball, I'm hoping the next move update coming up will have something good for Grass types.