When you say “if your stack was simpler” do you mean “if your problem was trivial”? I’m always interested in simpler ways to do things, but solving distributed system and data governance issues tends to involve putting things in different places.

If you're not going to mention what it is then you come across as snarky.

Do tell us what you think a "modern" approach would be.

Deploy everything using a cloud native architecture and have all services internet facing, read about "zero trust networks" to understand more about securing such things.

Maybe there are "data governance issues" stopping the internet facing thing from happening. But if not, that's a more modern approach then three tier network segmentation.