No, it isn’t. That was the case in SCALE Cobia and before, but it was one of the headline changes in Dragonfish to allow ARC to consume (almost) all RAM–which it should be able to do; why would you want to pay for dozens of gigabytes of RAM, only to leave them unused?
But, of course, that depends on ARC being evicted when the RAM is needed for other purposes. And if that isn’t happening, that sounds like a bug.