Yet another misrepresentation from Ron.
Ron's quote, which is a review of the research, not the research itself, discusses issues with the proxies but does not invalidate the proxies. The review goes on to say, "We can be more certain of how and why Earth warms or cools over decadal and multidecadal timescales ... In general, physics-based climate models accurately reproduce proxy estimates of our climate’s history over the past millennium."
Ron's cargo cult take that it's thermometers and not greenhouse gasses is his own, and his alone.
To quote the paper itself:
To place recent warming rates into a long-term context, we calculate 51 yr running GMST trends from the unfiltered reconstructions. The different reconstruction methods agree on the magnitudes of multidecadal trends over the Common Era, as shown by the narrow uncertainty range.
In other words, there is uncertainty but the range of uncertainty is narrow. And Ron's review of the paper says physics-based climate models, apart from the two largest volcanic eruptions of the Common Era, accurately reproduce proxy estimates.