If you add backstays, I bet you will reduce load on the servo/mast joint. I use only backstays (no shrouds), and have not lost a mast yet. You'll have to devise a way to let the mast rotate while supporting the backstays, of course. But you've showed enough ingenuity so far to make me believe you could figure out how to do it.
Boyle's 1930's article has a lot of good info for today's modelers, I feel. He's the one who first exposed me to the idea that backstays are sufficient.
Boyle's 1930's square-rigging tips: