OK - the easy way to measure high power is to let
it rip into the dummy load via a high loss coupler,
or maybe off the "isolated" port of a ring combiner.
200kW sounds like a radar pulse. Anyway, step 1
is to get a suitable sample of a sane size.
Next is the frequency. If the scope is up to
it, a direct measure will do. Otherwise, use a diode
detector, and then a lower bandwidth scope can deliver
the pulse envelope.
Unless..maybe I misunderstand.
Are you thinking of some sort of stand-alone instrument
that connects via a thru-sample head, and delivers
the answer on a display?