Firstly, none of those are double deltas they are cranked arrows with (more, comparatively) signature increasing trailing edge geometry.
Now for the main part — who said anything about subsonic cruise (at least outside of the beginning and end phases of a sortie)? If you are subsonic, you will die. What is so hard to understand.
IMO it wasn’t just the missiles. As early as 2019 if not much earlier, the PLA would’ve known J-36, ALHCMs and ALHGVs were all coming. And now they know that air-breathing hypersonic SAMs and AAMs with phenomenal range and speed are in the pipeline too (plus kill webs including dozens of CCAs, UCAVs, ISR UAVs, AEW satellites etc.).
Because you seem so wedded to the prior epoch (honestly, how many months ago did I put forth the no-brainer about what the PLA’s preference for missiles to be very fast, rather than stealthy and slow, would mean for the likely planform, we didn’t even have to wait for a podcast from the trio) — I will put it simply… a supersonic VLO bomber (possibly in a double delta J-36esque planform) is going to be far more survivable in the future, than a subsonic VLO flying wing (including these ELO and ULO terms you’re introducing). In fact, you could even use the former to hunt down the latter (just like how the J-36 will be used, as one of its many mission sets).
If you recall my comments from just after 12.26, when I coined the term “Air Cruiser” (which was screenshotted, placed in a chinese-language mil blog post and received praise, including from one of the trio and apparently a designer at CAC) — I spoke of how future air combat will begin to resemble naval warfare at the turn of the 20th century, might be worth reading (I noticed you only joined this forum in like January 2025, so you may not have read them).