I know preciously little about competitive battling, but I agree that it would be a good idea to introduce a buffing move to Grass that doesn't also buff fire. I could see something like "Primeval Glow" a fairy move that embodies the (modern) fantasy concept of an untouched world were forests were free to grow and tended by fairies/elves. It could be like a weather effect and buff grass and fairy type attacks.
Also kinda thinking Grass should be re-balanced to lose its weakness to flying (seriously, what?) and resist Fairy (fairies, spirits of nature are less willing/capable of harming it)
The Grass type needs more love.
Even though it is not the best, grassy terrain does what you ask. Sunny day is still better because of abilities like chlorophyll and moves like solar beam, while grassy terrain only boost grass moves and boost the defense of gogoat (only if he has grass pelt as an ability). I also dont understand why flying is super effective against grass, I heard because hurricanes can tear trees from the roots and birds eat fruits, but if thats the case flying would be strong over everything, and grass would be weak to everything...
Well there is Grassy Terrain. Its effects are minimal now, but if we get a Grassy Terrain setter (which is quite likely, given that we now have an Electric Terrain setter in the form of Tapu Koko) and more Abilities like Grass Pelt, we could see Grassy Terrain teams gain viability in Doubles (Especially since it nerfs EQ, which could also give a benefit to some of your non-Grass Mons).
And I don't think Grass needs its resistances altered, or Ice for that matter. Last Gen finally brought the Type chart to a level of balance it hasn't had since Gen 2, so there's no reason to tinker and experiment with it and risk throwing that balance out the window.
Grass has always been the Type that is easy to raise, but difficult to master. It has some of the best resistances and worst weaknesses, while also having incredible advantages and woeful disadvantages on the offensive side of things. This is why Ramos was so utterly easy to beat in X & Y. When you're fighting AI and you understand Type match-ups, most encounters with Grass-Types are a joke. But competitively, when you play around their weak points, Grass-Types can achieve some pretty awesome things.
Ice may be weak defensively, but that's the point. It is amazing offensively (4 Types are weak to it, and nothing [barring Shedinja] is immune to it, even with Abilities factored in), so the poor defensive nature of the type helps to balance that. Not every Type is meant to have a multitude of weaknesses and resistances. They all are different, possessing their own little quirks, and that's what keeps things lively and invigorated.
Grassy terrain is good and will surely get better (or so I hope), but at the moment no ability has been shown to control or benefit from it. Is highly probable a "grass type" Tapu koko will get a grassy terrain summoning ability, but until then... The other very high advantage grassy terrain gives is a 30% chance to sleep secret power (relic song is the other only move to damage and sleep, but it only has 10% chance).
And I have to disagree on the type chart being balanced, fire types became even more threatening thanks to their resistance to fairy, fairies are almost on the same level as dragons while this guys are still quite powerful, steel got a nice buff, but bug and ice were heavily damaged. Dragons may have lowered a bit of power, but the type chart is just as broken as before. A few changes could help both while not damaging 2 types too much: ice resisting dragon and ground (they are at the moment very powerful mons due to their very few weaknesses, and ice was meant to counter dragon long before fairies appeared anyway), grass resist fairies (Orphalesion gave a nice explanation of why this may make sense, that and also fairies have many grass support moves/abilities in flower veil and flower shield -yes, flower shield is a fairy type move, no, it doesnt affect fairies at all, only grass-). This way ice is still very frail while at the same time still being threatening, and grass would get a little buff defensively while still being just a worst version of water type (really, water type has advantage over fire, ground and rock, and grass has advantage over water... ground and rock, the difference is only one type, and guess which one is better due to being much more resistant?). Of course, this is just an opinion... is not like gamefreak will change the type chart soon, not until a new type is introduced, or if they, for some reason, see fit.
And ice is not amazing offensively, it may be among the top 7 or 9 but is not amazing, while at the same time being on the bottom 3 or 4 worst defensively, being only rock and grass worst than it (but rock at least has a much more offensive presence): fire, ground, fight, steel, fairy, rock, and even dragon are better offensively, dragon may be only super effective against itself, but only steel resist it and fairy is inmune to it, after that everything is hit normally.