Did it take him less than two years to learn how to fly J-20? Back in mid. 2017, he only knew how to fly J-16 and J-10C
Are you saying two years is long or short?
I also don't recall, in 2017 did we get him specifically saying he was not yet able to fly J-20s?
For all we know he could've been training to fly J-20s at the time, or maybe he took even less than two years to learn to pilot J-20, not to mention we don't know his operational "level" compared to other pilots currently.
In other words we know nothing about how long it took him to train to fly J-20s and very little about his level of experience in flying the J-20 compared to other J-20 pilots... So I think we can't make any assumptions.