Haswell can't run an Optane in it's cache configuration anyway, that was 7th gen or later. You CAN try to get ReadyBoost to enable, but, it's not going to make much of a difference. Swapping the SATA SSD for a faster one won't make much of a difference as you're still more interface bound, and the EVO 860 isn't a bad drive to begin with. You are likely I/O bound. While the cores are showing very high utilization, when they are stuck waiting for I/O, it's counted as being busy, so you have artificially high utilization.
Something else to consider: are you still running with all the security and vulnerability mitigations enabled? Those mitigations absolutely murder I/O throughput. The i5-12400 will be a massive I/O upgrade for you. Unless you are running the 5960X, it's an upgrade in every possible way for you, from I/O, to L3 cache, single core throughput, multi-core throughput, RAM throughput, etc. Even with the 5960X, you're still looking at better single core throughput and in 90+% of cases better multi-core performance. It also has very hew performance hurting mitigations as compared to Haswell.