You can have a very complex networking infrastructure with very simple proxies and network segmentation. What specific feature do you have in mind. Load balancing and resource synching?

Often there are proprietary solution to proprietary problems you would otherwise not have in the first place.

I used AWS for a long time but I am back to hosting myself. What arcane network requirement would that entail? I don't think there are benefits even for government scale problems.

Anything involving private links to other organisations, cloudflare or API management to multiple endpoints scattered over on prem and hosted. I would hope you could avoid most of the pitfalls by avoiding the proprietary solutions but sometimes there is no feature parity between host services and you might be stuck.

The private links in Azure are particularly specific.

I mean, networking in general is difficult and complex. While most of my work is in the "systems" realm of IT, my formal education was primarily in the networking side of things with systems as an "also-ran". The complexities of public clouds like AWS and Azure isn't so much new complexity in networking, but a deliberate change in vocabulary and implementation of existing concepts to justify the higher salaries of those certified on a given cloud. After all, if it was the same process to implement, say, HAProxy on AWS as it was on-prem, then the illusion of "new" is shattered and customers might realize they're just paying more money for their same infrastructure, but with shiny new terms and a more consistent API/CLI experience.

After you translate the vocabulary, the process is pretty similar until you get to security items, like ACLs or packet-inspection firewalls. You're still setting up VLANs in the form of subnets, routers in the form of transit gateways, sites in the form of VPCs, inter-site connectivity through peering connections, you get the idea.

If there's one thing I've learned in my IT career, it's that most "new" ideas are just rebrands of existing concepts, and that the real expertise comes from being able to translate marketing-speak into concrete, interchangeable fundamentals. Public Cloud is, largely but not entirely, no different in this regard.