axfrdns is a confusing mis-nomer; the daemon handles all TCP DNS queries too. TinyDNS will truncate any UDP response that doesn't fit in 500 bytes (it also doesn't implement EDNS0), leaving it to be handled by axfrdns. That's about 4% of all DNS responses going on my data.
To generalize my point; DOS is a very significant risk to DNS server availability these days, and the first and best defense is to have a fast server (Knot's target of 500k qps is in the right ballpark). djbdns is single threaded, single process and doesn't even use epoll/kqueue, it's just not up to it and tops out within a few 10k qps, axfrdns won't get close to that.
https://github.com/abh/djbdns/blob/master/byte_copy.c is a good example of my earlier point too; last time I profiled tinydns it spent a lot of time in vanity routines like that; the libc implementations are factored to CPU instructions and are much better.
No disagreement with your points about Bind though.
