This somewhat goes back to the question of what the goals of the PLA are.
I don't think the PLA are under any illusions about the importance of air power, and if the aim is to comprehensively compete in high end air combat against the likely capabilities that will be present in the region, skewing heavily to 5th and 6th generation platforms seems like an obvious necessity to be honest.
Keeping 4th/4.5th gen platforms around is unnecessary if the industry and funding to support their replacement with 5th/6th gen is there, because as previously I wrote, you are already paying for the pilots and ground personnel anyway.
That 2035 orbat would comprise 2300+ Chinese 5th/6th Gen aircraft.
Given the likely capabilities of the opposition in the 1st Island Chain in 2035, air superiority would be a given on Day 1 and in a long-war scenario.
And in such a scenario, there will be a lot of demand for heavy bomb/missile truck sorties.
For this, 5th/6th gens are suboptimal compared to 4.5 Gens
The Flanker airframes are better suited for this and have already been paid for.
So why not keep the J-11B around, given that there presumably would only be 600 J-15/J-16.
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Also consider that if we're talking about an additional 1900+ Chinese 5th/6th Gen aircraft in the next 10 years, it makes sense to have a lot of them operate on carriers instead of being land-based.
Let's say the Chinese Navy does add 6 new aircraft carriers by 2035, which the Lowy Institute and the AEI/Foreign Affairs magazine is now repeating. If all the carriers switch to 5th/6th Gen, then the overall split could be:
a) ~500 naval aircraft
b) 1400+ land-based aircraft
The 1st Island Chain should still be easily secured for both Day 1 and a long-war scenario.
But now, the Chinese Navy should also win blue-water naval battles past the 2nd Island Chain, on both Day 1 and in a long-war scenario.
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And remember that in terms of this 2035 force structure:
1. the Chinese Navy would be comparable or slightly smaller than the US Navy
2. the Chinese Air Force would be (at most) 66% larger than the US Air Force
This should be affordable, given that the latest price surveys indicate the Chinese economy is now twice the size of the USA.
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I've long said that it would be a mistake for the US to adopt a hostile containment policy, instead of engagement