The original proposal was to have a one design mast and that the masts were to be identical (or as close as possible) the expectation was that the scenario the Finns enjoy would occur. A finn sailor can order from one of several builders a mast with exact bend properties and get it.

A Finn mast is actually harder to build with those properties than a T mast. The Finn mast is not circular as you say, but is much more wing like than a T mast or even a A class mast.

Finn sails are amongst the most carefully built sails in the world, luff curve alterations of 1/2mm are common. Having less righting moment actually makes the mast more critical and getting the bend right even harder to do.

How do I know this? Well I coached the Aus Finn team...

The problem with variations in the carbon masts is that it put us in the same spot we were in with the alloy masts! We used to have different mainsails for different alloy masts and now we still have to make different sails for carbon masts.... It would have been much better to be able to take sails to each boat (masts) and have no difference between them. Also would have been cheaper....