I think LM21's question is not trivial and can't properly be answered by the anecdotes and vendor ratings etc.
I would agree with jonpaul reply 8:
The Tee and Pi impedances per network are cast in stone and element values can be measured (o/c , s/c, thru) or calculated, for example
https://www.everythingrf.com/rf-calculators/attenuator-calculatorNest step is to connect networks in series as LM21 requests, and solve using Kirchoff.
That will give the current, voltage and power in each element of each network.
Above is how old guy like jonpaul, myself would have done it on slide rule or calculator ( and now easier in sim) ,
but young guy would probably use S-parameters and get the same results.