There is of course a slight chicken-egg-thing here: If there was no (dynamic) branch prediction, we (as in compilers) would emit different code that is faster for non-predicting CPUs (and presumably slower for predicting CPUs). That would mitigate a bit of that 10x.

A bit. I think we've shown time and time again that letting the compiler do what the CPU is doing doesn't work out, most recently with Itanium.

The issue is with indirect branches. Most branches are direct ones.