Yes, the thing you didn't consider is that if I am a new user and fire up my brand new install of Bitcoin in five years, I'm being paid nothing for having to download 10GB of blockchain even with pruned transactions, and might just give up. Blockchain bloat has a higher price.
Sigh.
Ok, fine, so do a back-of-the-envelope for what THAT cost is.
Big +1 to d'aniel for doing the work of actually calculating a number, that is very helpful.