Well, you are making the case for 80 bits security level.  Bitcoin set out to have a 128 bit security level.  Once that principle is adopted (for good or bad reasons), it is good to stick to it.  If you don't, you have inconsistent security requirements, and inconsistent burdens.  Some calculational and storage burden would be due to people sticking with 128 bit security level, while other parts would only give you 80 bits security level and punch holes in the burden that was paid for elsewhere.  I can agree with you that maybe one should have put bitcoin's security at only 80 bits level.  That would have shortened quite a lot of things (room on chain, processing capacity, network capacity etc....). But Satoshi put it at 128 bits level (that's why the ECDS keys are 256 bit length).  Once you go for that, you have to keep it uniform, or you have inconsistent safety and burden.