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.
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