It's different in Spain but I think it's unfair to say Vela's flourishing because of the league and not make that same distinction for Griezmann who plays in the same team and league. Why is he bound to be an awesome player?
Vela played 62 games for us. I don't know how many of them he started but I it wasn't a lot from what I recall. When I consider the amount of starts Denilson had and see that it can take a full season in the first team to see a players true potential (Ramsey) I don't think it's enough. As for his loan spell with West Brom, you should probably check out the amount of games Gibbs, Ramsey and Wilshere played when they were loaned out during a January window. Vela played 8 games but got 2 goals and 1 assist. Know idea how many games he started but it's not bad considering Wilshere played 14 games for Bolton. Unless it's a season long loan, I don't recall any of our players racking up huge appearance numbers.
Either way, that was then this is now. He might just be finding his feet at the right time. His international record for Mexico as a youth was always impressive. No idea if he wants to come back considering recent reports but he's an example of what annoys me about our youth development system.