BUT the simplistic issue is that the chainplate which attach the 'lowers' usually are 'bent' to meet the angle of attachment of the lowers to the mast. That bend causes whats know as a stress riser (weakens the load bearing ability) AND also causes flexure in the lower plate in the region of the 'kink'. Flexure (of a cantilever) is an entirely different stress regime than the pure tension of an unbent plate that attaches a cap shroud.

Its the usual bent configuration of the 'lower plate' that makes it "geometrically/mechanically weakened" and actually MORE prone to fatigue failure.

FWIW - I really admire the chainplate system design in the newer Beneteau boats ..... all are straight, in *pure tension*, no flexure ..... and NO bends; very 'elegant yet simple' structural engineering that should have a very long 'service life'.