I’d say $500k per year on AWS is kind of within a dead man’s zone where if you’re not expecting that spend to grow significantly and your infra is relatively simple, migrating off may actually make sense.
On the other hand maintaining $100K a year of spend on AWS is unlikely to be worth the effort of optimizing and maintaining $1M+ on AWS probably means the usage patterns are such that the cloud is cheaper and easier to maintain.
In my experience amounts are meaningless, what counts is what kinds of services you need most. In my current org we use all 3 major public clouds + on-on prem services, carefully planning what should go where and why.
On the other hand maintaining $100K a year of spend on AWS is unlikely to be worth the effort of optimizing and maintaining $1M+ on AWS probably means the usage patterns are such that the cloud is cheaper and easier to maintain.