great post! key points for me:
1. 100 IXes alone would get 56% IPv4 and 61% IPv6 prefixes, but ~14% reachability
2. little uniqueness between exchanges: not many new prefixes after the top 5
3. for outbound-heavy networks IXes are great, but to attract traffic they are not (edit: applies to automatic peering via route servers)
Post author here
For inbound traffic, they're completely fine. This is only looking at the route servers. You can almost certainly receive 50/50 traffic ratios if you do bilateral peering. This post only covers the " automatic peering " services that IXs offer