We moved about 400 VMs across AWS and GCP to Oracle Cloud spead across 4 regions. Our approach was to first move our applications to rely only on Load Balancers, Block/Object Storage and Compute from the cloud. No RDS, BigQuery etc. This required a slight increase in SREs/DevOps resources.

Once we did this, the move was fairly easy (the exception being having to write our own auto-scaling logic as the built-in one is very limited). Overall we reduced our cloud spend (even accounting for the additional staff) by about 40%. Bandwidth is practically free and you are not limited to specific combos of CPU/RAM (so you can easily provision something with 7 cores and 9 GB RAM). Another big factor for us was that compute costs in OCI don't vary by region.

I will not recommend using any other managed services from OCI besides the basics (we tried some and they are not very reliable). We've seen minor issues in Networking periodically (Private DNS, LBs or interconnectivity between compute instances), but overall I would say the switch has been worth it.