I expect the Kunpeng (ARM) may have received a higher speedup compared to FeiTeng (SPARC v9). I'm not privy to their software, but I used gentoo (in the fairly distant past, working at the university surplus so I had access to odd computers). I futzed with it on x86 (of course -- no x86-64 yet that long ago), DEC Alpha, DEC MIPs, an SGI MIPS, a HP PA-RISC, Motorla 68K, and Power/PowerPC (both an IBM and an Apple). More recently I installed Chrubuntu on an ARM Chromebook (retired, unfortunately the chassis, battery power connect, etc. all kind of disintegrated after a while.) I've kept up on the state of things since I don't feel at all tied to x86-64 (although I'm running it at present.)
In short, x86-64 probably has highest coverage, most CPU optimizations, llvm optimizations, programs with MMX/SSE/AVX optimizations in them,e tc. ARM is a close second. PA-RISC, m68k, Itanium (before it was dropped entirely) had least coverage. Alpha, SPARC, MIPS, kind of in the middle. So just saying, given the general software ecosystem it was probably easier for them to get the 2-3x speedup on ARM compared to on SPARC (although SPARC is no slouch and it does have "Visual Instruction Set", some MMX/SSE/AVX-like instructions to use for that type of thing, so if something can take advantage of those but doesn't it'd get a nice speedup when it does.)
As for China coverage -- what can I say? Having a country have to kind of establish this stuff from scratch is fascinating reading. It's not like they're neglecting coverage of western chip builders, they just are not having to get things going at this kind of pace so there's less to cover.
As for the embargo backfiring? Well, so far it hasn't hurt them too much -- having to make chips with tech that is like 5-7nm instead of 3-5? Just not a big deal. I'd say it's backfired if they successfully get smaller-nm scale production working before the 5-7nm tech is too obsolete; it will have just pushed them into producing their own chip production technology where they otherwise would have probably just bought hardware from ASML. If they don't succeed in dong this, then it hasn't backfired and was successful.