The paper mentions JIT multiple times, lockdown mode disables JIT. I hope someone else can confirm it but it appears it would be mitigated in this case.
It seems like JIT would make the attack easier as faster code will get more accurate timings but it doesn't seem to really stop the attack.
It's not just faster code, but also having more control over it. The JIT engine is more than happy to put a hundred data-dependent instructions right after each other; an interpreter makes this harder.