If the cams were off even 1 tooth either direction it would kick a CEL and the car would run like dogshit. May even PTV if a tooth off retarded. Don't know what this cam degree talk is about, there's no degreeing VCT cams. Phasers only install one way, can't mess that up unless you're *really* special. Have seen improperly torqued cams sheer the dowel pin off the phasers before, but that would be catastrophic. Have seen people mess up the phaser spring doing limiters or lockouts, but again it would throw CEL's and VCT would not function properly.
If the cam grind is off, it's in the grind itself and would be comp cams bad. Can't see the car running great for a time, and then showing problems, if the grind was bad. Bad tensioner or guide is top most likely if it is a cam timing issue.
I agree with a leakdown test, but I'm not sure why 1 bank would present with issues over the other. The odds all 4 rings on 1 bank were incorrectly installed seems flakey in theory. Why are there issues now vs day 1? I think a bad guide/tensioner is more likely. Even if the heads/deck weren't milled correctly, it would be a constant, not a random down the road. If there were a problem with a head it would also be a constant, if not at least an isolated failure of a single cylinder. All 4 at the same time suggests timing.
Comp Cams isn't QC perfect either, I had a SN95 friend put cams in his GT, when we went to install we double checked part numbers to identify LH from RH, and found we had 2 RH cam shafts. Brand new in the box lol. Needless to say, he got some goodies from Comp as well as a LH cam.