From what we know the USB port for external drives on PS5 is slower than the NVMe M.2 so you won't be able to run PS5 games from external drives (you will need to transfer to internal NVMe or use the original memory). Now comparing a USB Stick to SSD (be it NVMe in capsule or any other way through USB) it will mostly depend on speed, but for PS4 gen games it possibly will be all similar.
duduspace11 "Well, since we are estimating costs, Pokemon Red/Blue did cost Nintendo about $50m to make back in 1996"
http://gamrconnect.vgchartz.com/post.php?id=8808363
Mr Puggsly: "Hehe, I said good profit. You said big profit. Frankly, not losing money is what I meant by good. Don't get hung up on semantics"
http://gamrconnect.vgchartz.com/post.php?id=9008994
Azzanation: "PS5 wouldn't sold out at launch without scalpers."