International football is generally much more open than Serie A. He's not someone to unlock a line of defenders, we have seen evidence enough of this.
Imagine Juve randomly played a bunch of Serie B teams over the season, you'd see Bern get a chance to shine and pad his stats. Also, I think Mancini improves a lot of attacking players with the slick football he has got Italy playing.
Also, if you look at the goals he has scored - Liechteinstein (2), Estonia, Greece, and Ukraine in a friendly.
When I was looking for his international goals I couldn't help but laugh reading some of the content on his Wiki:
Sacchi in 2017:
"He [Bernardeschi] doesn’t use his right [foot] much and he needs to improve in that, if you only have one foot you risk being predictable and the opposition can shut you down more easily. I’d say he dribbles well, he takes on a defender and goes past them with agility and imagination. He also has a good shot on him, he sees the goal, takes aim and the result is always dangerous (maybe to pigeons - JJ) A great player? Calm down, calm down. I’m describing a lad with notable talents, but one who has to mature and be helped. For example, he has to learn how to get into the rhythm of the game with consistency. To be great, you need to have an understanding with your team. ... Bernardeschi needs to do better in that regard, less individual technique and more collective technique."
Scout report from 2017:
"His decision-making has also been cited by pundits as an area in which he needs to improve as he gains experience"
Over three years later unfortunately those things are still relevant.