I'm growing less clear about what your complaint is. If you're just pointing out a methodological problem in that one paper then I agree with you. If you're claiming that the whole field is so messed up that no one even realizes it's a problem, then the paper that I linked looks like a counterexample to your claim. The authors seem to recognize that it's bad to make ad hoc choices about which proxies to use or which years to apply them to, so they came up with a systematic procedure for selecting proxies (it looks similar to taking all of every proxy that correlates significantly with the 150 years of instrumental temperature records and then averaging those proxy estimates together, but more complicated). And because tree-ring data had been the most problematic (in having a poor fit with the temperature record), they ran a separate set of analyses that excluded those data. They may not explicitly criticize the other methodology, but they're replacing it with a better methodology, which is good enough for me.