... and Zimmerman played how many games in the minors?
Rendon was an advanced hitter, who came from college. He's shown that his bat is elite -- and yeah, he should still get some more time in the minors, but it's not like we're talking about an 18-yr-old that's only played prep games.
Zimmerman had also played his college career at 3B without missing huge amounts of time with injuries. Rendon hasn't played a full baseball season for over 2 full years. His junior year at Rice he was the DH most of the time due to injuries and he missed almost all of last year.
The kid needs the AB's. It's not a matter of capping him. It's a matter of getting him used to the pro game on a daily basis. Why rush that when you have Zim at 3B? The only spot for him potentially is at 2B if Espi struggles horribly and he's never played 2B outside of a few games. I just don't get the need to rush him. A full year in the minors with a September call up is perfectly reasonable.