He sounds entitled. He wasn't a guaranteed starter under Wenger so what made him think Emery would guarantee him playing time? I like Jack and have had sympathy for him in the past but I think he's made a poor decision. Again. It's just like when we decided to go on loan to Bournemouth because Wenger wouldn't assure him of playing time. That decision to go out on loan backfired because he had an average season, still ended up getting injured and that put him in a shit position upon his return to Arsenal to negotiate a new contract. You can't come back off loan with 2 assists under your belt, average performances and think you'll get back into the first team. It exposed him and dropped his stock around the country.
Emery can't guarantee him playing time but if he'd at least tried to prove himself and hang around to learn from him, it would be better for him in the long run. Unless he's going to a bigger rival club, I don't see the benefit of taking a step down to a lower league club when he still has a lot to learn and could benefit from Emery's knowledge. He should have at least hung around for a year and then make a decision.