It doesn't matter what term is used to describe Julio. What matters is he is a 3.5 WAR talent that is projected to produce ~14 WAR over the next 4 years at a total cost of $37M. That represents around $75M in surplus value.
The chances of regression are already factored into that 14 WAR projection. That is his 50th percentile outcome, which means there is a 50% chance he does better, and a 50% chance he does worse than 14 WAR. He could be better, he could be worse, or he could get hurt...but that is true for every single player and every single projection system.
This means he is "worth" a prospect whose 50th percentile outcome is a 3.5 WAR player for more than 4 years since those "future potential wins" are inherently more risky and thus less valuable than wins Julio provides today. From the same FG article, Joc Pederson is projected to be worth 12 WAR over his team control years, so he's not worth Julio. Gioloto is projected to be worth about 18 WAR over his team control, so that is the type of player who is a worthy return for Teheran. Bregman at 20 WAR, Benintendi at 18 WAR, Mazara at 20 WAR...those are the types of returns that are "fair". The Braves should be looking to win the trade if it's done at the trade deadline, so it needs to be Benintendi plus something, or Moncada with his projected WAR of ~23.
That's what Teheran is "worth", and FG literally just displayed it in table form. So for them to then turn around and say Teheran is only worth a 45 FV prospect is asinine.