While this might be true if you try to AXFR large zones I think most people who have large zones have solutions to this, it's just like scaling anything else.

While this might be true if you try to AXFR large zones I think most people who have large zones have solutions to this, it's just like scaling anything else. For example there's IXFR which is helpful when doing dynamic updates. Alternatively don't use DNS for transfers -- there's nothing forcing its use, except for talking to clients -- SQL replication works (e.g. with PowerDNS), or the approach most spam blocklists take and rsync zones around for serving by a special server (rbldnsd); DNS just becomes a common query protocol because every client supports it.