IMHO, the aircraft helmets I have seen (and occasionally used) are next to useless. They are typically a very thin shell, with almost no internal padding, and in the event that you actually hit something hard, I son't believe that they would do anything to reduce the overall impact that your skull experiences.
I have one of
Ivan Campbell's helmets, which to my layman's eye seems rather less flimsy than those you describe. As noted on his website, his products feature:
a lightweight, high impact resistant, kevlar and carbon fibre blend inner compact hard shell; outstanding head comfort with a felt lined, closed cell, energy absorbing, memory retentive, moulded lining
I admit that I would be happy to see aviation helmets featuring
Snell certification.