The J-35A has virtually no apparent advantage over the J-20 (let alone J-20A) to justify it's procurement
Sure there is. Superior stealth, enhanced multirole capabilities, and lower cost and maintenance ease itself is still an undeniably significant advantage.
The J-20/A's prowess in A/A is also undeniable. But it comes at a hefty cost (pun intended), and its equipment and itself isn't designed for being multirole. The J-35A provides PLA much of the J-20/A's A/A capabilities at a fraction of the cost, while giving the PLA something that can stealthily complete SEAD/DEAD missions cheaply without risking an important A/A asset. That is something the PLA desperately wants, as hinted from Deino's source.
cheaper complementary fighter to fill the ranks.
...of PLA multirole spots, yes. What, the JH-7s, older J-7/8/10/11s have gotta retire eventually.
Especially when J-20 production may have reached it's maximum output for the near (and relevant) future.
Not when it's switching to J-20A production, and there's still a lot of spots to fill. Ones that an expensive, pure A/A fighter won't really be suitable at.
The PLAAF doesn't need two aircraft that are totally equal.
You're right. Fortunately, they're not.
The J-35 will simply slowly take over for the J-16 in PLAAF service, while for the PLANAF the J-15T and J-35 will constitute that...how do the Americans say? Hi-Lo mix.
As I've said, J-16s will be the latest ones to go. They've still got fairly old fighters, and it doesn't hurt to expand their ranks. After all, the USAF still holds a numerical advantage.
You generally don't see air forces operate two equally capable fighters for the sake of it.
Correct. That's why the J-20/A and 35A serve different purposes.
Point being, by nature of being an advanced stealth multirole fighter, the J-35 couldn't be different enough to th J-20 to justify it's purchase by the PLAAF
Tell that to the PLAAF, who seem to be very eager to get their hands on the J-35A. And as established, they're very different.
unless it's much cheaper (less capable)
Cheaper doesn't directly suggest less capable overall.
and thus can be procured in bigger numbers simultanously to the J-20.
Which has a point, as established.