Flying should hit Grass neutrally and instead hit Ground super effectively. This removes one of Grass' 5 weaknesses and adds another weakness for Ground, which hit 5 types super effectively while being weak against only 3 types. This helps strengthen Flying's advantage against Ground and also removes one of the 4x weaknesses of Bug/Grass.
Bug is terrible offensively, hitting 3 types super effectively but being resisted by 7 types. I think Bug should hit Fairy, Fighting, Poison, and Ghost neutrally. Fairy already had only 2 weaknesses with 3 resistances and 1 immunity, so this should help balance its defensive capabilities. Fighting maintains its position as a strong offensive type, Poison still has 4 other resistances, and Ghost still has 2 immunities and 1 resistance with 2 weaknesses, so these changes shouldn't be too huge. But Bug should be happy, now being resisted by just Fire, Flying, and Steel.