I think that is a good point that just because a guy starts the year in the majors it doesn't"t mean they will make it the whole year. Khris Davis was one that made the opening roster, didn't do well, was sent to the minors and then came back in the summer and was the Brewers best hitter.
However, to your second point if a player is doing really well it is a double edge because they may get a pick but they may regret losing the player a year early.
Maybe seeing all of these contracts given out the Brewers may be willing to offer long term contract earlier to these young players and the extra year doesn't mean much.
Will be interesting how it plays out and what their strategy is.