Resting aside all the political trash talking and national pride, I still don't think it's fair to say PLAN's subs are mostly just junks.1st of all, Besides the well-known 091, 092, Song and Kilo, China is getting along with the Ming-Class modification programme quite well. The newly-built Ming started since 90s and many have been built under the programme. The sub is not only capable of sinking the surface targets but the undersurface ones as well. I'm not sure if it's can fire C-801Q underwater but it's not that hrad if you got 533mm tubes and target-acquisition figured out. The fact, Modified-Ming can fire the newest Yu-6 and Yu-5 can prove itself quite capable as a modern sub. Although the overall upgrade is not clear but the sub is using many newest technology borrowed from Song and its capabilit should not be easily dismissed.
Tactically speaking, it's much easier to find subs leaving out of its pen and around your fleet defense circle but it's an overstatement to say even the most advanced navy can track Chinese subs in realtime in all areas.
So there goes my point again, "there is always a discrepancy between the theory and reality", that's called the "fog of the war".