There are plenty of synthetic 5W30s that don't have especially impressive CCS test results.
The data is a bit old, but in 2011 the PQIA had Mobil Special 5W30 conventional at 5836 cP at -30C for CCS while Royal Purple 5W30 was at 5562 cP and Castrol Edge tested at 5544 cP in 2013. These all meet the spec for 5W30 (6600 cP at -30C), of course, but M1, Pennzoil Ultra (RIP), Shell Formula, and Havoline synth 5W30 were all under 4000 cP in CCS testing. RP 5W30 was 45% more viscous in -30C CCS testing than that killer Penn Ultra 5W30 (which also had a super low 6.6% NOACK loss) and over 40% more viscous than M1.
It's just one data point at a low but not insanely cold temperature (-30C is -22F), but there is a lot of variation among synthetic 5W30s and not all of them knock it out of the park against conventional oil.