Sure it might be able to reach the 2IC today but how much time the Y-9 based ASW/MPA can stay near the 2IC to be meaningful? And how about to go beyond the 2IC? And the Indian Ocean?
I believe everyone agrees that China will need to have new MPA/ELINT/AEW&C/etc based on a narrow body with turbofan engines. If a fully domestic C9x9 variant won't be available soon, will such needs disappear somehow? The answer will be no of course. Then what options will China have for backup?
If the Y-9 and Y-30 bodies were so good for the MPA/AEW&C/etc. of the next decades, China would not have developed the KJ-3000 as we see today.
#1 - The Y-9-based GX-15 is both the best and readily available option to China right now and in the foreseeable years to come - And that China is able to mass produce them entirely on their own. That's a FACT.
#2 - Producing more GX-15s (and have them retrofitted with mid-air refueling capabilities), alongside other measures (including shutting off one or two engines mid-flight to conserve fuel) are the best/rational/logical actions China could do at the current juncture. Developing a brand new ASW aircraft based on the Y-20 platform is not one of them.
#3 - If anything, building more Y-20B MRTTs and YY-20Bs that can be made available for refueling the GX-15s (in conjunction with in order to extend their mission duration and combat radius would be a much more effective (and on top of that, readily-available) solution, rather than trying to develop a Y-20-based ASW aircraft from scratch.
#4 - In contrast, developing a Y-20-based ASW isn't just taking away the limited manpower, resources and money that would better off going to other higher priority/critical projects, but also occupying Y-20 production slots at Xi'an AC that would otherwise better allocated towards the production of more Y-20B MRTTs, alongside KJ-3000s and specialized Y-20B tankers in the future.
#5 - Why did you move the goalpost to beyond 2IC and also into the Indian Ocean? As a matter of fact, the P-3s, P-1s and P-8s only have combat radii of ~2200-2500 kilometers with 3-4 hours of on-station time. They certainly won't be able to conduct meaningful patrol missions beyond the 2IC if they're based in mainland Chinese airbases without mid-air refueling or refueling stops somewhere in the 1IC/2IC, let alone into the Indian Ocean.
#6 - Why are you putting ASW in the same league of discussion as AEW&C? Both the KJ-700 and KJ-3000 occupy different tiers in the AEW&C domain of the PLAAF and PLANAF. Both the KJ-700 (小平台大预警) and KJ-3000 (大平台大预警) aren't just having different features and capabilities to one another, but both of them are complementary to one another. The KJ-3000 does NOT replace the KJ-700. On the other hand, there is certainly no need for separate tiers of ASW aircrafts.