I don't even think they have as much pace as you assume. Salah's 33 km/h top speed for instance is almost average. Great timing, movement and transitioning makes players look fast. If you actually look at the goals they scored against you, none of them involved outpacing the defenders. Also, look at how easy it was for Diaz to get his goal and assist. He could keep it very simple. When was the last time one of your attackers just needed to keep it simple to create a great chance? Sancho needed to take out 4 players through dribbling and passing to create that chance for Rashford while at Liverpool, the transitional moments seem so orchestrated. They make the right runs with the right timing and the players know which passes they have to play at which moment and with which urgency to get into the dangerous areas. They see when there's an opportunity to pass to a player between the lines and then accelerate the play. I mean, look at the first Salah goal, that's the perfect environment for Sancho - one player coming short, play it into his feet and get it back, another one running inbehind with the right timing, etc. And all this isn't new, it's the same recipe that made Dortmund so successful under Klopp.
If Sancho would be playing for Liverpool, he'd start at LW 100% with Mané playing false 9. He'd flourish in this system to an extent less talented players like Dias or Jota aren't capable of. And he'd look much faster and aggressive than he currently does for you. Klopp always had players like Dias at Dortmund (albeit with lesser quality), like Kuba or Großkreutz for instance but the ones to really excel under him were the technically excellent players great in tight spaces like Reus, Götze, Gündogan, Lewandowski, Kagawa, etc. Typical Pep players actually.