This doesn't surprise me.
I was looking at a newish Ribcraft 5.3 with a nice shiny A-frame the other day and I noticed the forward legs of the A-frame aren't fixed to the deck, but bent rearwards and welded onto the rear tube sections at the transom mounting plates. The set-up lacks the rigidity of an A-frame with forward legs fixed to the deck.
Any decent fabricator should be able to weld some webs between the tube/flat plate which will reinforce the attachment point. It would be better to fix them down to the deck somehow, although this would be a bigger job.
Nice boat, BTW - looked like you were having a rite larf out there.