I won't comment on the nitty-gritty specifics of the J-11D's price/performance ratio, but I do see an issue with your assertion that the quick advent of 5th generation aircraft can somehow offset the cancellation of the J-11D program.
The production of the J-20 is still <24 airframes a year (probably close to single-digit figures at this point), which would be woefully inadequate to replace (or even complement) existing 4th generation aircraft such as the J-10 & J-11, much less the hundreds of obsolete J-7 & Q-5 that still serve. With the J-11B ending production (if not already at this stage), the PLAAF would have no air-superiority fighter that could bridge the gap between the 4th-gen J-11B & the J-20. It would take no less than a decade for the J-20 to completely replace the J-11X, and an additional 15-20 years for it to supplant the J-10s (assuming a 24 airframe/year production rate from the get-go).
There are ways around the issues you described, and some of the issues you described aren't really issues at all.
For example,J-11Bs can be upgraded with radars and avionics to J-11D standard without having to build a new aircraft to be able to maintain a fleet of twin engine, long range, advanced 4+ generation fighters.
If J-11Ds are indeed not as cost effective as J-10Cs where it matters then the production rate of J-20 doesn't have anything to do with the air force turning down J-11D.
We also cannot yet discount what other fighter programmes the air force may have down the line that may influence their force structure, whether it's actually buying a variant of FC-31, or maybe buying a combat capable variant of JL-10, or even maybe a version of JH-XX, all of which would in turn may influence the future force structure in a way we do not yet know.
And this is all in context of the original possibility that J-11D may simply not be cost effective in the face of threats of the foreseeable future as compared to other aircraft like J-10 variants
Put all that together, and I think the question we should be asking ourselves is not whether J-11D is definitively going to be cancelled and why, but rather if J-11D is cancelled then are there any plausible reasons for it? And I think the answer to the latter question is yes.
At this point, I still think that there is a possibility (a likelihood, as a matter of fact) that the J-11D program is still alive. The entire cancellation rumor stemmed from one post from "Pupu" which stated that the PLAAF is seeking to purchase only the J-20, J-10C/D, & J-16 for the next few years. Furthermore, there have been rumors of a fourth J-11D prototype being built in late 2016.
Who knows. I personally am not convinced if the rumour of lack of J-11D purchase in the next few years is true or not.
However, if the rumour is true, I think there are a number of very reasonable explanations for why the air force may have declined J-11D.