Sysadmins at places I've worked have used "defense in depth" as an excuse to create layer upon layer of frustrating hoops to jump through in order to get any work done. I'm pretty sick of it. One perfect layer is vastly preferable.
A security design that takes advantage of multiple layers and compartmentalization is your ally against attackers. They love networks with hard shells and squishy insides. Once they are in via a service, no matter how innocuous, they can move laterally to the real targets with impunity.
But ultimately this kind of stuff is a culture issue. Culture issues are hard to fix but it's usually the root cause of bad blood between operations and development. It generally needs to be addressed on both sides though. It's really easy to think it's just a bunch of grumpy and possessive ops people but those behaviors are often rooted in how the dev teams interact with them. Things like punting releases over a wall and calling it a day, not participating in oncall duties despite causing many outages and a disparity between how credit (for releases) and blame (for outages) are assigned are often cited as issues that create what devs think or irrational BOFHs.
Strong passwords, two-factor auth for privileged services, access control policies (ACLs/firewalls), access logging, etc. are all requirements of any secure network. And that was just "off the top of my head on a Friday" kind of stuff.
Ah, hello, every manager that has ever made a decision causing the problems people further up are grousing about.
The point of defense in depth is there IS no "one perfect layer."
If not, you have relatively little to complain about.
And, I'll add, if you're a developer, we'd all prefer you just crank out perfect code. That way we never have deployment issues, get paged for outages, never have to work around poor architecture or assumptions that don't scale or aren't load tested. thanks!
That's the problem.