I find board stiffness to be absolutely critical. Especially as the rest of the kit gets stiffer putting more pressure on the board.
These days I have a little 2 person test. Set the rig on the beach, foil up, one person stands on the board and tries to move the foil around, the other puts hands around the plate connection. If there’s movement you’ll feel it!
Try it! Things get flex way before they break! What do you do to assess the condition of your board?