Too strong draft for the Princess is not good either. Maybe it can work with more draft, but I know that
@kennyp2339 has added 2 key dampers (stove version).
I'm not sure what the chimney height is for him, and I don't remember whether the Princess insert has a metal or ceramic cat - the metal one has smaller "holes", and with strong draft fly-ash sometimes flies into the cat. Clogging the cat is therefore sometimes an issue with too much draft, and more so for a metal cat.
I don't remember your response (or I'm mixing different threads by different posters) but I thought you did not run the Regency at full blast? Therefore (if my memory is correct) I don't think you should be worried about the heat output of the Princess. The Regency choked down is going to be quite far below the Princess at full blast.
What is your hesitance about the damper? I did not get that yet. To me it appeared that the feedback you got from this one dealer employee ("can't say, so don't do") was not correct. A stove is meant to work in a system with a certain draft. If the system is not drafting enough, folks add chimney height. If a system is drafting too much, one has to decrease that for safe operation. Cutting chimney height off is most of the time not an option. A damper is.
Both stoves are from good brands.