If one has their library on Google Drive, where is Plex server running from? Guess you still need a local machine running of some kind for the server? Same for other automation tools like sab, sonarr, radarr etc.
For what it's worth I would not currently put my library in the Cloud for a couple of reasons.
1) I don't tend to change my NAS/Storage often, so whilst my hardware could die out of warranty, so far things have been OK. Fixed upfront cost then no constant monthly charges. Mind you my NAS unit was £650, and the drives I have installed also came to about the same, so I could go a lot of years on Google Drive for the same cash.
2) More importantly, whilst my download speed is alright at 150Mbps, upload is only around 30Mbps, it would take an incredibly long time for me to upload a meaningful library in size.
3) I don't need to back any of it up as none if it is irreplaceable.
4) I do quite like having the ability to watch my stuff offline, if my internet dies then at least I still have access to the library. You can cache some stuff in Plex, but then you'd have to know to do that ahead of time.
If I had better internet then it would definitely be worth considering when it reached the time to decide whether to get a new NAS or not if this one dies.
Whilst they haven't cottoned on and prevented people going over the 1TB cap, that is not 100% going to stay the same, and at some point they could start enforcing those quotas. I guess 20TB of cloud storage is usually more than £9/month.
From benefits I suppose there are some beyond the no-upfront cost thing, one is backups not needed necessarily (although even Google could lose data?), and another might be that you could share the library elsewhere without using your data or local servers to serve remote clients.
Your reasons don’t really stack up, or at least you seem to be overlooking some quite obvious stuff.
1) At the current monthly rate, £650 buys you almost 7 years of GSuite, that’s ignoring saving power costs and any replacement drive costs/down time on your NAS or the costs to expand it as/when.
2) You get $300 of free GCE credit, a VPS with gigabit or even 10Gbit connectivity is a few €/m from a wealth of different providers, im sure you can see why your local upload speed is largely irrelevant when you can easily dump 7-70TB/day for minimal cost and pay by the hour or month to do so. If you run a local Plex server as you presumably do now, it’s pretty straight forward to point it at any media source, local or otherwise.
3) Kind of a moot point, versioning and backup are better to have remotely than not.
4) How unreliable is your internet connection? In a rolling 12 months over the last 30? years I suspect I’d be unlucky if I have lost more than a a day in a bad year. Power cuts probably have a greater impact in most years, either way it’s a pretty minimal % of time (0.0027%/day).
Do you honestly believe that the biggest search engine and number one ranked site on the planet isn’t aware of how it’s products and services are used? I mean it’s been 4? years, perhaps they should google that or look at the slew of YouTube videos on the subject (a google owned business that adds thousands of hours a day of video)? Also remember the timing, it just happened to be a thing that happened around the time Amazon was offering its own service, then withdrew it.
Sign up to GSuite for Business and you get $300 credit that can be used for GCE, just like any other VPS, you can run what you like (Sonarr/Radarr/SAB etc.). If you want a more detailed breakdown, have a look at Plex Guide, it automates a lot of the process of deployment/configuration, or do it manually, whatever suits you best.