Ret Paladins, How viable will they be?

Yup. No 15% Damage from Vengeance. Holy Shock has a 30 second CD ontop of a huge mana cost.

It has a gimmick for PvP but is perfectly fine as a hybrid healing spec for dungeons/raids.

The Shockadin spec you may be referring to is the “Spelladin” which is 31 ret 8 prot 12 holy and focuses on white attacks, spell damage stacking and consumable use.

If if you really mean Shockadin then I suggest checking out Durnos videos and watch him OOM himself in every 1v1. As far as I know he started the ‘Shockadin’ trend but he does it much better in his second video.