Where I would differ from you is that your post suggests Esse has sufficient talent, and that if only he could develop the appropriate mindset he'd be good enough for the palace first team. I've seen a few posts to that effect.
I haven't seen this natural talent in Esse. I don't see any real signs of quality there. I've looked back at his best bits at Millwall (at least as far as YouTube has them) and whilst he's not incapable of being effective, at least as that level, I couldn't see what the club saw in him.
I wonder sometimes if they had just decided to sign a young up and coming player from the championship as it had worked so well before, but without really assessing the individual player.