Best Of

You've drawn a 2-pipe, direct return system and if you're willing to do the work, it's a good choice. However, if you change it to an indirect return system, it will self-balance, with or without TRV's.

Does anyone still install Monoflow systems? Such a PITA to purge.

I would avoid this idea. Some day a new boiler will be needed and someone will decide that reversing the the direction of the water thru the system is easier that running a pipe about 3 feet longer in order to save a few dollars. At that point the oversized lower temperature radiators will become the hotter radiators and the correct size radiator when it was first on the loop, will not get warm enough to heat that room. Baseboard radiators are the only radiators I would recommend using the series loop, and as long as you don't go over 65 to 70 feet of aluminum fins in a loop, then you don't really need to oversize anything based on a lower water temperature. here is one example of wanting to reverse the flow years after system was installed

Another reason not to series loop radiators is TRVs can be added easily.