If you switch to a PC, you will really find out what pain is, starting with a subscription system that will nick you for Apps that were included in previous versions. There are millions of Mac users that update without problem, even on machines 6 or 7 years ago. Try updating s 6 year old PC with a current Windows version. Without the manufacturer making sure all the drivers work, which they won't because they have had dozens of new machines since that, it is a rocky road. Especially fun when a trojan virus has usurped your machine and is preventing anything from being updated.
Apple does an amazing job considering. Could they employ more people to solve the problems that are caused by individual configurations? Sure, but the line has to be drawn somewhere.
1. Determine if your machine works correctly on a different network. If not, look for routers plugged into routers and such on your network. Routers and advanced switches cache information that has changed.
2. Remove and recreate access accounts.
3. Re-construct the keychains.
If none of that works, restore your backup and try the installation again.
good luck