I don't think they ever really intended for disc to 'do dps' to any meaningful amount. They intended for us to heal through doing damage, but for our main job to be healing, for us to be a competitive healer, and for our damage contribution to be minimal. They're well aware that a class that is a true 50/50 split between healer and dps is never going to be viable.
My impression of the nerfs to trinkets and food damage procs was to keep them balanced relative to other trinkets and food, in terms of how much they increased our healing, not our damage.
Consider a comparison between
Naglfar Fare (3 RPPM) and
Oakheart's Gnarled Root (2 RPPM)
On average, assuming negligible healing from the HoT component, the Nagalfar Fare will do 75k*3= 225k Healing per minute = 3.75k hps
On the other hand, assuming it wasn't nerfed Oakheart's Gnarled Root will do 125k*2=250k damage per minute = 4.17k dps.
Now, 44% of that damage is converted into atonement healing, so ignoring overhealing and assuming zero mastery we would get 4.17*0.44 = 1.83k hps, PER atonement.
We can safely sit at a minimum average of 5 atonements, so at minimum that will provide 1.83*5=9.15k hps, ignoring overhealing. This is why our damage procs have been nerfed by ~66%, because if you take 33% of that you get 9.15*0.33 = 3.02k hps, as well as 1.37k dps. This is assuming a minimum of 5 atonements when it procs, and obviously it won't be 100% effective healing, but you can see that it's now roughly in-line with the 'healing' trinket's value.
But we have the potential for it to proc at 15+ atonements in a raid, which would give us 3x the value it would if it procs at 5 atonements, or up to 9k hps. That makes it potentially 3x better than the healing trinkets and that's AFTER it was nerfed. If it wasn't nerfed, and procced at 15+ atonements, we could get up to 27.45k hps from it, which would be almost 9x better than a 'healing' trinket. However, the random proc makes the likelihood of getting the full potential out very unlikely, so on average we won't be getting nearly as much. So considering the RNG, I think a 66% nerf was a little high, but a 50% nerf would probably have been very fair.