I used to read ThousandEyes's annual free reports on networking capabilities and measurements across the Big 3 cloud providers, which were quite comprehensive in terms of covering various scenarios [0]. I don't think they publish those anymore.

With cloudping.co, it isn't clear from the website, but it seems like the inter-region latency they measure is over the public Internet. The Big 3 run their own backbone across all their DCs around the globe, and so I reckon, those numbers would look vastly different if traffic was instead relayed through those uncongested backbones.

With AWS, the cheapest way I know (in terms of development time and cost) to accomplish inter-region over their backbone is via Global Load Accelerator. The clients connect to GLA at the nearest anycast IP location advertised across 150+ AWS PoPs. You can then play with endpoint-groups, connection-affinities, source/port tuples to control routing traffic to different backends in various regions.

We used this technique to prototype a VPN with exit nodes in multiple countries but entry nodes closest to clients at every AWS PoP. It worked quite nicely for a toy: https://news.ycombinator.com/item?id=21071593

[0] https://www.thousandeyes.com/blog/top-takeaways-cloud-perfor... (2019)