Jo Adell doesn't have a big enough role to grow
When the Angels selected Jo Adell in the first round of the 2017 MLB Draft, they expected him to be a cornerstone in the outfield playing alongside Mike Trout. Through the first four years of his MLB career, Adell has proven absolutely nothing. He's been a liability both at the plate and in the field, and has now put the Angels in a tough spot.
The thing with Adell is he's currently out of options. This means the Angels have to keep him around in the majors or risk losing him through waivers if they want to send him down. The Angels won't risk running him through waivers, so barring a trade, Adell is going to be on the Opening Day roster regardless of how he does in Spring Training. Unfair? Maybe. But that's the business of baseball.
Adell performed better than he ever had in the minors and eventually had a full-time role carved out for himself when Mike Trout landed on the IL. Unfortunately, Adell went on the IL himself just a couple of days later. He'd return in September but played just 17 games this season. In the 62 plate appearances he had he wasn't too bad with a .706 OPS and three home runs, but he did strike out 25 times. An alarming amount of punch outs.
Strikeouts have been a constant for the young outfielder and is a big reason why his play hasn't translated to the majors. The Angels hope he'll improve with his plate discipline, but it's hard to do that when you don't play every day. As of now, the Angels don't have the room for him to be an everyday player with Taylor Ward, Mike Trout, and Mickey Moniak pencilled into the outfield.
Adell could have a couple of starts each week replacing Trout when he takes a day off or replacing Moniak against a lefty, but he's not going to even have the chance to start regularly without an injury. It's hard to expect real improvement from Adell if he can't even play every day.