Mono-grass is a mediocre type, but in combination with the right secondary type it's great. Ferrothorn, Ludicolo, Celebi, Virizion and Breloom wouldn't be nearly as good if they were mono-grass.
Grass is useful if you know what you're doing.
I beg to differ. Grass is the most common 4x resistance in the game. It has its uses (namely getting rid of things like Gastrodon and Rotom-W) but it's not in the same league as attacking types such as ice, fighting and rock.
You just specifically said that Grass has its uses. And you have to know what you're doing to take advantage of that.
Grass is far from useless. Especially in a metagame full of Water types and rain teams.
I'm not easily impressed; I'm usually oblivious to whatever's in front of me. Stunfisk is the epitome of monstrous majestic legendary creatures that spew fire.