How about rendering the majority of sweepers, walls, baton passers, ground, water and electric types useless while forcing your opponent to either switch into hazards or lose a pokemon?
Like I explained earlier, the overwhelming majority of erufuuns just try to sub seed. Sub seeding erufuun is terrible. It is the wrong way to use him. Good erufuuns are rare, so not many people have experience with its potential. I want to call it a 'defensive pivot' but i'm not sure i completely understand what that term means.
As for erufuun 'damaging' something, it creates a leech seed/toxic/encore prison while entry hazards are down. It forces your opponent to switch around. Yes, you nees heatran and vappy or some other type equivalents to support it. So what? Does doryuuzu suck because it needs ttar/hippo? Requiring support is not a negative trait; if all your pokemon aren't supporting each other to begin with, your team probably isn't doing so well.