softy wrote:I do believe all those holes must weaken the structure.
Nup. Not how bicycle protective helmets have ever been designed to work.
They are not designed to protect from crushing of your skull by a two-tonne vehicle. Even my old MSR would not have done that. They are simply impact energy attenuators ie. they absorb the impact of a fall onto a hard surface. The strength of the helmet structure does not matter, as long as it basically stays in one piece.