Probably a different answer for each site. I'm not a DNS expert but I think you're right on both counts. Having failover also requires a duplicate CDN architect

Probably a different answer for each site. I'm not a DNS expert but I think you're right on both counts. Having failover also requires a duplicate CDN architecture at the fallback location, which is an increase of costs in time, money & maintenance for relatively little benefit. Often there's a fair amount of background integration with a CDN, and each function slightly differently, so it's not simply plug & play.