Yup. Understood. Cavitating is common on our Glycol loops here at the office as well, so I'm familiar with the general concept. (Just on 5HP pumps, like the pair right above my office, rather than a CPU sized one. )
In this case, the Monarch loops are closed systems, so even to get to the point of trying to add any fluid, it would require breaking the loop. So I might as well insert a reservoir that can get the port for bleeding air or adding fluid. And the fact that the Monarch trips the overload protection on the 1000W PSU, and it's the only thing on it, suggests there's truly something struggling and the heat isn't being removed from the system as needed.