Noone loves tempo. Ye olde shaman was the perfect example of TEMPO class, what blizzard did to him? Nerfed into pile of useless shit with weird mechanics.
AND THEN they added one more perfect example of tempo class called "dh" because shaman was no longer able to show that amount of tempo as he shown before. So they set up shaman from tempo class to SLOW AND WEIRD SHIT and just replaced it with a new class.
Which old shaman decks did you have in mind? Originally, Shaman was about overcosted overload cards. Later, Shaman has been tier 1 on the back of various OP cards (FF, TFB, Tunnel etc.) but I think Rogue has always played the pure tempo game better (clearing and building board on the same time.)
I feel DH is stepping on the toes much more than shaman, which is more about board presence and elemental spells. Heck, the "outcast" and weapon/attack synergies could be seamlessly introduced in rogue instead of making a new class.