I've cleared about 3 heroics pre-3.0 on level 70 in tbc with just 4 shamans, and many first/second bosses in other heroics. With Thunderstorm tho, no trash in the old tbc content would be a problem, so the only thing you need to focus on would be bosses. And thunderstorm rotation and dps to deal with all trash. However, in wotlk level 80 heroics, that tactic isnt going to work anymore. Not only are there many mobs immune to the knockback. mobs have vastly superios Hp and simply cant be nuked down all that quickly. Whereas I usually killed on 1 trash mob in two rounds, another in another two rounds, killing two trash mobs before they could reach me with an earth bind placed proper in heroics at 70. That tactic isn't cutting it anymore at 80 for me atm. :P

Also, bosses arent quite earth elemental tankable anymore in most situations. Some bosses still can here and there, but not as reliable as in tbc, where you could earth elemental tank probably 80-90% of the bosses without too much complication.

Plus the boss fights in heroics at 80 are much more scripted, which makes the standard nuking tactic to not function either on many of the bosses and will require more control over the fight, which can be found in having a proper tank in the party. :P