What has a player got to do to be a great one? Sancho is exceptional, I think I've never seen such a talent in the Bundesliga bar maybe Götze - and even he wasn't as good output wise as Sancho, although similarly talented. If he keeps improving at his current pace, sky's the limit.
I don't think he's moving to England, though. Liverpool has no issues in his position, City is out of the equation for obvious reasons, no other club really has the perspective to lure him. I also think he'll eventually play as a LW not a RW since someone with his technique, dribbling ability and close control needs to cut inside. He's already better on that side, IMO. This makes it even harder to predict where he'll end up. Madrid has Hazard, Rodrygo and Vinicius in that position, so only Barca would make sense perspectively but they are linked more to Neymar and/or Havertz currently. Maybe they'll buy Neymar and Paris will try to sign Sancho as a replacement, who knows.
Will be interesting to see where he'll end up. The club who'll sign him from Dortmund can consider itself lucky as hell.
I tabulated the stats
1. Kagawa
a. 17 goals 14 assists as a 22 year old ~~2 dribbles per game ~~3300 minutes
b. 12 goals 2 assists as a 21 year old ~~1.3 dribbles per game~~2100 minutes
2. Mkhitaryan
a. 23 goals 32 assists as a 26/27 year old ~~2.6 dribbles per game~~4300 minutes
b. 5 goals 7 assists as a 25/26 year old ~~2.6 dribbles per game~~3100 minutes
c. 13 goals 10 assists as a 24/25 year old ~~3 dribbles per game~~3700 minutes
3. Gotze
a. 7 goals 8 assists as a 19 year old ~~3.5 dribbles per game ~~1700 minutes
b. 8 goals 16 assists as an 18 year old ~~2.5 dribbles per game ~~3000 minutes
Sancho
a. 16 goals 17 assists as a 19 year old (mid season) ~~2.8 dribbles per game~~2425 minutes
b. 13 goals 19 assists as an 18 year old ~~3.3 dribbles per game ~~3000 minutes
Based on age, rate (per game), dribbling, and end product I would argue that Sancho is #1. And he's 19 years old. You wouldn't need him to replicate his stats over in England. If he produces at 3/4 of those stats when he's in his prime, that would be a huge success. You should look at his age and his performances in Germany as a development stage for him. This is not even close a comparison in leagues (so don't take offense German fans), but if you were to take a Championship player doing well as a 19 year old, and then buy him, sure he won't hit those same heights initially (hello Zaha), but he will grow in ability that he will eventually start to produce at that level in the tougher league. Not sure why Sancho isn't the same. That's if you want to make that argument. I wouldn't make that argument because I'm fond of the Bundesliga, but even if you were to look at the Bundesliga in that manner, there is no argument to be had around the idea that "Sancho won't produce at that level in the PL."
On the other hand, someone like Mkhitaryan was already 27 years old when he came to the PL. There was no more development left for him. Completely different from Sancho's situation. Plus, look at Mkhitaryan's other seasons in Germany. He looks more like a 1 season wonder when it comes to that kind of end product than someone who jumped to a new level in ability.