> software now is much more complex than it used to be

I'd say software now is much more complex than it needs to be. It's made to ease the life of the developer, usually an inexperienced one, at the expense of the user.

> IMO, for security reasons alone, it's no longer realistic to expect software without at least occasional updates.

If people would stop rewriting things that already work fine, we'll run out of vulnerabilities at some point. Or, if you must rewrite them and have a good reason to do so, at least use a memory-safe language. Even C++ is much better than C and raw pointers. Anything is better than C and raw pointers. Yet all major OS kernels and most userspace components are written in C and use raw pointers and vulnerabilities in those are being found all too often.

> If you root your device, doesn't that mean you will no longer be able receive Android OS software updates from the phone manufacturer?

It often means that. :( But it is not that bad for some devices. Geeks from Lineage community regurarly update closed vendor code in the LineageOS. So if you are lucky and Lineage is well-supported on your device, you can still have root nowadays with up-to-date vendor blobs.

For example I rooted my Xperia XZ2 Compact and I am quite happy with it. By using Magisk and Magisk Hide, I am still able to use Google Pay. At the same time, I can use Titanium Backup and f-droid root extension to let f-droid install updates automatically. I hope this device will last me for a long time as I don't see many alternatives - most other phones are too big for me, too old/slow or unsupported.