I would be curious if you could provide any examples for the issues you cite. They sound plausible to me, especially around peering disputes or in various Asia countries, but I wonder how in practice this looks in like a traceroute for the amount of added latency etc.
I would suspect some of non-optimized scenarios are eyeball network operator decisions on their networks that DNS providers and others do not have much control over. Like, Cloudflare resolves an IP that is closest to them, which is likely also the closest to the end user (and the eyeball ISP), but the eyeball ISP BGP path to that resolved IP takes a roundabout path because of their own BGP policy because $reasons.
We have many BGP workarounds to avoid interconnection points with some of our tier 1 providers and DT because as our providers tell us, discussions with DT to add capacity are a non-starter. We've been relatively stable through a tier 2 provider through Lumen to DT though... for now. Very similar to Cogent in some regions.
To each their own. I mostly figured out why, and I did not want to create too much tech debt in my homelab with brittle split-DNS and PostUp/PostUp wireguard configurations. I already had ansible and templates setup to move back to the VM and docker-compose. I did learn a fair bit on CoreDNS, so that was a worthwhile experiment.
I had challenges with split-DNS in my homelab k3s cluster trying to do this. I ended up just putting the apps in docker-compose on a VM that has static routes for my local homelab networks. I looked at tailscale to solve this since it has a kubernetes operator, but tailscale doesn't fit my use cases or work well with all of my devices.
I would suspect some of non-optimized scenarios are eyeball network operator decisions on their networks that DNS providers and others do not have much control over. Like, Cloudflare resolves an IP that is closest to them, which is likely also the closest to the end user (and the eyeball ISP), but the eyeball ISP BGP path to that resolved IP takes a roundabout path because of their own BGP policy because $reasons.