Yep, I already pointed that out to you specifically! It's superlinear in the mempool size (well, ignoring caching)  But thats unrelated to f2pool/antpool and the other SPV miners, as they're not ever calling createnewblock in that case, as they're mining without even validating.   One can mine on a validated chain with no transactions while waiting for createnewblock (which is what eligius does, for example).  I also pointed out that this is trivially optimizable, but no one has bothered previously.