I've been there and done this and it's effective.

It's an imperfect solution for all of the obvious reasons. I think even the most junior engineer could point out the flaws. I won't insult HN readers by naming them!

But also: effective at some things for near-zero cost. It's probably more effective at "segregating your traffic so that Low Priority Service A can't starve out High Priority Service B" than overall scaling but, sometimes that's what you need.

    paying the price of deployment complexity

For us, there was essentially no increase in deployment complexity. There was a small one-time increase in network routing complexity. Essentially requests for "www.foo.com" were routed to one group of servers and requests for "api.foo.com" were routed to another group.

The alternative was decomposing a large monolith. A goal we also pursued. But what you describe was a valuable stop-gap as we undertook that multiyear effect.