Fishin said:
Water/Ground has no synergy? How about ground completely eliminating Water's Electric weakness? And how is Vire using EQ or Cross Chop a point against Swampert? That just puts Swampert in the same position as the Grass/Fire against Metagross in your previous example (actually, better, since Swampert is immune to Vire's STAB while Grass/Fire merely resists Gross's or is neutral to the very rare Zen Headbutt variants). Zapdos is a different story but unless it carries HP Grass they really can't do anything to each other, except Swampert is being useful and setting up SR while Zapdos is just doing 20-some % to Swampert.
What I meant was that from an offensive standpoint, Earthquake offers little to no support for Waterfall. The two hit (Electric, Steel, [Rock, Fire,] and Ground) pokemon hard, but are both resisted by Grass.
Before we get to "Ice support," look at Fire/Grass:
(Grass, Bug, Ice, Steel,) (Water, Rock, Ground) and are both resisted by Fire and Dragon.
To Water/Ground, Ice support adds Dragon, Flying, and Grass
To Fire/Grass, Ice support adds Dragon and Flying.
In other words, Fire/Grass with Ice support (only HP Ice) only has to worry about other fire types. Give it Flash Fire and even these can't counter it effectively. Ice support also happens to wail on Flying types that would normally switch right in, although its worth noting STAB Fire Blast does more to opposing fliers than SE HP Ice.
The long and short of it is: If we give this a single decent offensive stat and good defenses, this can cover pretty much all of its weaknesses with Super-Effective damage. If it can retaliate a 3HKO with a OHKO, it will always win, and since most of the things that resist one STAB are weak to the other, it offers much greater synergy than Water/Ground.
I'll try and make a better example:
For Fire/Grass I'll just randomly call it Pyrelm.
Enemy Meganium switches into Swampert. Swampert's only option is to Ice Beam or run. Neither of its STABs can do anything to what resists it, and meanwhile it is susceptible to 4x damage.
Enemy Torkoal switches into Pyrelm. Neither really threatens the other. Pyrelm can either try and Subseed and have it spinned away, or try using a Hidden Power. If it had Flash Fire though, Torkoal would be completely SOL.
Enemy Salamence switches in to Pyrelm. Here Salamence has a large upper hand. Pyrelms best shot would be HP Ice. In the meantime, Mence's most powerful move would be either Aerial Ace, HP Flying, Dragon Claw, or Draco Meteor. Roostmence is particular completely shuts out Pyrelm. Nonetheless, if it had enough defenses it could stall out Mence with Subseed, or, depending on status and Mence's set, cripple it with Will-O-Wisp.
Were this a sweeper, Mence would force a switch 100% of the time and probably get a Dragon Dance in. If we give it the defenses to take a hit, even seemingly perfect counters aren't foolproof.
Now I grant you that Swampert is a known quantity and Pyrelm isn't. Either way, Grass's litany of support moves makes even safe switchins risky, and the more hits it can take, the better it does its job.
Ice weakness doesn't mean that a Grass type is suddenly a bad anti-bulky water. A 252 sp atk (which we'll never see on a standard bulky water set, btw) Milotic Ice Beam doesn't even 2HKO the standard 252 HP Celebi.
Celebi has 100/100/100 HP/Defenses, and 600 BST. It isn't a reliable example, which is why I usually prefer Meganium. Milotic also has the option of just Hypnosis'ing Celebi, which is only ineffective due to Natural Cure. It isn't as if you can switch Roserade into Starmie or Milotic Ice Beam with Impunity. Nevermind Tangrowth, Exeggutor, and Torterra, who all have STAB and wherewithall to send most Bulky Waters to the grave in one shot, were it not for Ice Beam stomping them into the ground as they came in.
And as I stated before, there's no Grass Pokemon with Fire STAB - that alone sets it apart from other Fire types, but there are a variety of other factors that will, as well. Part of the purpose of this project is to create unique Pokemon - if you think we can't even do that given such a good platform as Grass/Fire, you must not have much faith in CAP.
I have plenty of faith in CAP, I just don't think creating yet another Fire typed sweeper (this time with STAB Energy Ball/Grass Knot) isn't really unique as much as it is just another fire-type rehash.