Well USB can only power a small mostly 2.5inch external drive and cannot really spin most large 3.5 inch drives.
And once you want larger sizes or more reliable enterprise drives which are in most large external usb drives you need power. If you are happy with a smaller ( and most likely less reliable ) 2.5 inch drive usb only is of course more convenient.
I have 3:2:1 for my crucial data ( pictures of family and travels and digital documents like tax returns). Basically one main copy another copy on an old nas with shucked drives not connected to the internet and one cloud copy. It is worth it because I would hate hate to lose that data.
I have 2:1 for my media. Just a local copy . If the apartment goes up in flames or a freak lightning burns it down I will have to re-download it again or I will live without it and ghats fine. For a long time the media had no backup but just raid and snapshots to protect against hard-drive failures and dumb user errors.
It’s all about your means and risk appetite.
Past performance is a terrible predictor of future performance. Ssd prices dropped a lot since the pandemic since demand dropped and the factories are still there. As usual this normally means that new factories will be delayed and prices will be relatively higher going forward for a while. Now the longterm trend still favors ssd but 2022 Is a shitty year to base your price projections on