Well every player we lose is technically a loss, but Joseph has a much lower projection than Tocci does. If Joseph puts up an 800 OPS that is below average for his position and adding in the defense, significantly below average. And the odds of Joseph at his age becoming an 850+ OPS hitter are pretty small.
With Tocci he can become an above average player with only a 725 OPS in CF paired with good defense and above average speed on the bases. He is also 4 YEARS YOUNGER than Joseph, turning 23 this year while Joseph turns 27. So Tocci is much, much more likely to improve than Joseph. These are basic facts that people project players on.
And your contention that Tocci getting above 700 in OPS only makes him a marginal starter is wrong. Look at Ender Inciarte. His career OPS is 733 and he has produced 15.4 WAR in 4 seasons (though more like 3.5 in playing time). If Tocci is over 700 he might produce only 3 WAR per season, but that still qualifies as at least average in terms of starters.
Why would a deep organization like Texas choose to keep him if he is considered a non-prospect? They are less deep now but the cost of keeping someone on a 25-man roster is only worth it for real prospects. We might not have room on the 40-man roster for him, but he is still a significant loss for the team. In hindsight some sort of trade (for Tocci) or to clear spots on the roster potentially should have been made.
