I'd think, it is basically 1x Tank + 1x Heals + 3x Melee DPS.

So you have the disadvantage of being in cleave range.
Or getting hit by the majority of the bosses nasty AoE effects, as per the normal melee toons.

Think back to WotLK for a 3x Ret (DPS) + Prot + Holy, 5x Pally team.
Or the 4x Ret, 1x DK team, as that was all melee too.

3x Frost & 1x Blood is going to be so much faster on trash.
Bosses too, because of the massive DPS increase.
Depending on your gearing, you could even go Frost vs trash, and all Blood vs bosses.

You're not going to have survivability issues with:
- 1x Blood Tank
- 1x Healer spec'd Healing Class.

And the DPS from 3x Frost is pretty sick.