The bulk of the work is done by the GPU, not the CPU. During the benchmark CPU is only used to prepare the test in-memory images, it's not a heavily parallel task and it's not included in the benchmark measurement (doesn't affect the results). In other words, with OpenCL enabled the CPU utilization figure doesn't mean anything.
380 is an okay result for M1 Max, but we have some results reported by other customers that are higher, and I would expect that the beefy Mac Studio should provide the best performance and the least thermal throttling. So this result might be on the low side, but not obviously low. It could be down to what other things the system is doing. Have you tried rebooting your Mac, closing all the other apps, and then running the benchmark? It would also be interesting to do this after the system has been turned off for a while, i. e. when it's not yet warmed up.