I recently booted old (Freebsd 12) VM and was surprised how _much_ more performant (vs debian) its tcp stack is, even when just browsing.
Why not the TLS implementation? The video drivers and their kernel interfaces? The OS' process scheduling? A dozen other things that might be responsible for the perceived performance difference to one degree or another?
It feels like gamers who blame 90% of multiplayer issues on "the netcode".
It'd be different with data looking specifically at TCP connection establishment timing without a bunch of other stuff involved.
Had a wicked issue where a firewall was inspecting DNS requests and causing them to take almost 10 seconds to complete. Was hell on the SIP phones, and browsing the Internet was... Interesting.