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Yeah nah, one less fastener, but mainly, Shimano put the arms where the load is; big gaps at tdc and bdc, and even figured one opposing pair should be beefier than the other. It's optimised AF compared to any five arm spider.
Shimano's cranks balance lateral rigidity of the big ring against weight in the design criteria, everyone knows the best front shifting is on a Shimano crank...
Kimmo-
hear hear, but you confirm my point. shimano optimises and compensates its aesthtic choice of 4-arm design with beefier chainrings ( see tessalated ones on r7000)
The arms might be placed closer to stress areas, but as you say,that still makes the longer boltless section a thing to be adressed.
Shifting ramps and efficiency is another matter.
Glws
@Ordinata has a point imo, modelling cranks on solidworks or else doesn't change physics... you can go skinnier 5 arms or beefier 4-arms like shimano