Okay, I see your point, but our test harness isn't meant to be an absolute "max throughput" benchmark. every packet is parsed, corrected (if needed), and validated in real time (CRC32c, on-the-wire checks, deterministic network emulation, etc.).
If we ever want a true ceiling number, we could add a separate fast path (e.g, a dump-writer / sink that skips most validation) or validate after run, but that's not in scope right now. our scope was: (1) validate Pion/SCTP PRs and (2) compare performance against other branches and version. so for relative benchmark under identical conditions.
on head-of-line blocking: we have a pending RFC 8260 message interleaving (I-DATA) implementation, and we've tested with it; it helps reduce HoL on the sender side (especially around fragmentation). our benchmark tool has a flag to run with interleaving, and we tested it quit a bit. We plan to release it in Jan.