Limited catch radius. Focus drops. Lazy routes. Goes down first contact. All a team has to do to shut him down is focus on him. Better route running would go a long way towards fixing that, but I'm not gonna hold my breath on that one
Rams have better options for the slot than him IMO. So I think putting him outside at Z and making him be an actual WR is a good move. If he doesn't do the work to improve his routes and show an ability to take the top off, then reduce his snaps in the rotation and move him next year. He has the speed you want in that role so I'm going to wait and see whether he does the work to prepare and succeed in it.