We do the best we can with a limited standard that is difficult to modify. Archiving is always lossy, we try to reduce that as much as possible, but there are limits. People create web archives because they care about not losing their stuff online, not because they need an accurate record of transfer-encoding property in an HTTP connection. If storing the transfer-encoding is the most important thing, then yes, there are better tools for that.
"Archiving is always lossy" No.
The web is best-effort, and so is archiving the web.
I think he has more context than any of us on the limits of proxy archiving vs browser based archiving.
But also if you really need perfect packet-level replication, just wireshark it as he said. Why bother with WARCs at all?