Ok - if you want to talk PTR numbers rather than Cata numbers.
Then SoI is a chance of returning 80 mana, which makes it beyond nerfed when you compare it to Archangel or Telluric Currents.5) Which was overpowered and HAD to be nerfed if they were serious about "mana matters". But I guess some people love to be overpowered.
Now if you want to talk cata numbers, and really you should, then the main heal is up at 2.1k mana - around 10% more than the equivalent spell from a priest or druid. SoI is a chance of returning 900 mana, again far worse than either archangel or telluric currents.
Nobody disputes that mana returns from Seals was out of hand, but the reduction is to the point where it's near useless.