Well, TBC is relatively kind to Shadow Priests, and if you’re into doing those raidy-type-things the removal of the debuff limit actually makes it viable to take more than one Shadow Priest for both DPS and mana battery utility.
Ret Pallys though? Hmm… I dunno.
I levelled a Ret Pally in early TBC and it was still very much like being permanently stuck in the slow lane while other classes ran rings around me. They were Ferraris, I was a Reliant Robin. Then came the patch that boosted Ret Pallys into the stratosphere, and for a brief moment I was an absolute wrecking ball able to solo bosses - until I was nerfed back into the ground a few days later with an emergency hotfix.