Can ECDH peers waste each other's time at will? Peter Dettman notes that ECDH peers can waste each other's time at will. What does he mean? Can this be weaponized against Lightning nodes?
It was in the context of the peer sending an invalid point. The proposed scheme would not detect that immediately, and so would do extra (wasted) work. 

However the peer could equally waste your time by sending a valid point (possibly without knowing the private key) and just abandoning the protocol after you've done the work anyway.