-A lot of attention to IR masking, well over 5th gen average, despite having it harder(no stabilizers to work with). IR signature just doesn't work together with supersonic flight. Maybe sound as well, btw.
-Both are relatively thick birds, with quite a lot of wing on top. Especially Shenyang one, which more or less shares power rating with J-20(A), yet has way more body to her.
-Neither has vertical stabilizers and neither tries to cheat in a way visible with F-47 render ("V" wing...and that's before we truly know what's there in the back). J-20 (which we know for sure focuses on supersonic fight) had 4 just a decade ago.
-J-36, furthermore, intentionally goes for a really large iwb, i.e. it lets more work to be done by the arrow rather than by the archer.
Those are, of course, just my observations. It's totally reasonable with all that written that both can be faster than I currently assume. Or one of them.
But my current inner understanding is they're normally transsonic/low supercruisers(perhaps up to 1.5 for normal operating envelope, with mean speeds below m=1)), and their high wing sweep is less about speed, more about desired signature reduction.
Then, their power is mostly to help them get out of predicaments (bvr maneuvers, disengaging, slower pursuits), onboard energy/cooling, as well as to ensure fighter class take off and landing performance.
Higher speeds, not so much. They're undesirable, as those are aircraft that really don't want to be found or seen; blinking is not enough. Especially J-36, which is range-bound to keeping very low profile.
I don't disagree with those observations -- IR masking, large fuselage cross sections and IWBs (especially J-36), no vertical stabilizers... but I don't see how any of those can reasonably lead to the conclusion that they are incapable or not intended for supersonic flight at credible mach numbers.
If anything, everything you described somewhat applies for all aircraft -- technically there are few tactical combat aircraft which spend large amounts of time in supersonic flight, as they will bloom their signature. Prior generation/less stealthy aircraft would suffer from that arguably moreso than J-36 or J-XDS