You know what, let's dig into this
As fans we like to speak about "possession football" but lots of the coaches and players standing for this approach are very hesitant to use this term since it is misleading. And that's because possession is a byproduct of this style, not the objective. When Xavi was being confronted with fans being bored by Barca/Spain, he argued that the opponent was to blame for this because he parked the bus. This meant that it is much harder to find space, leading to longer possession phases. And that's hinting at the core of this style: In the end, it is quite simply the refusal to play "dumb balls". Instead everything is about control and leaving as little to chance as possible. You don't whip a cross in hoping that somebody nicks it in or gets at the end of a second ball. You don't take low percentage long shots. Instead you move the ball around, trying to create superiority and find space. But if you encounter the opportunity to play a dangerous pass with a high enough chance of success or go into a one on one, you absolutely go for it. So the style sort of defines itself by what not to do and instead making the simple decisions. And for this, positional play is the key because it enables you to play simple. Not only by standing in the right place but also by making the correct runs with the correct timing.
Now, if you are the underdog and play this way, the relation between "searching space" and "exploiting space" naturally shifts towards the latter because the opponent is committing more players to attack, meaning that you have to recycle the ball less time before finding the space you're looking for. So possession isn't really a decent indicator to judge whether or not a team plays possession football (re: Kiel). And this also goes the other way round: If you are by far the best team in the league, you'll naturally end up with lots of possession. But the question is how you try to overcome the defense of the opponent: Head through the wall or patience? On the contrary, if you encounter an opponent on eye level, you usually don't pin him back but have a much more open game in the middle of the pitch. And again it's the question control vs. chance - do you play risk averse long passes, hoping for second balls, or do you try to outplay the pressing of the opponent? "Possession" oriented teams will always opt for control and the "reproducable" play if given the choice.
So it's essentially "control vs chance" or "circumvention vs breaking through". They'll pass around until they spot the opportunity to create a chance in a controlled fashion ("possession as a byproduct"), not by playing the probabilities ("when crosses and long shots have low success rates, this just means we have to attempt more of them"). Of course there are nuances to this - for instance, City and Liverpool behave very similarly against the ball and in the immediate transitional phase afterwards but where Guardiol's team teans to utilize these transitional moments to get back into control of the ball, Klopp's rather tends to see the attack through until the end. But one way or another, both coaches these days are quite similar to each other.
Now, the reason why "possession" oriented teams like those two are so successful in league competitions is exactly that, control and reproducability. It's by far the best approach to make qualitative disadvantages count by eliminating as much of the factor luck as possible. So if Dortmund wants to maximize their qualitative advantages over the rest of the league bar Bayern, it should be their go to approach, if you ask me.