I completely agree with you first sentence but not agreeing with many of your points under that.
Online storage is not cheap. Well it might be for small amounts of data but it gets expensive really quickly if you want larger amounts. And that not to mention online storage speeds. Even with a good FTTP connection, many consumer and small business level storage services are still really slow.
If you want more than a TB of fast online storage, you're going to have to dig deep and if you can find it, then I hope your internet bandwidth doesn't become a bottleneck..
The games drive on my desktop is heading towards 1TB (SSD) and my photos/home video drive (HDD) is far off that either. Backing 2TB to 'the cloud' cost far more than buying a NAS with a few TB of HDD storage. Plus if my PC dies, I've got the option of a bare metal restore. I don't know any online provider that can do a 2TB restore in any timeframe that I can work with.
5G isn't going to fix the internet, at least for a decade. If the rollout of 5G is anything like 4G, it'll take that long for it to be cheap enough for the general public to use it in the manner it's intended and even then the service providers will limit it in some way.
256GB is fine for documents, emails, the typical music library and a few photos. Want to store some home videos and play a load of games, you'll be struggling. Read Dead Redemption 2 for PC requires 150GB on it's own and I have no idea what a 4k home movie takes up but I bet it isn't tiny.
Here's to 2TB SSD drives at sub £100 prices. Until then, most of my archive stuff and backups are going to held on (multiple) HDDs