I'd say you know what you get from them. Paulinho is a rather clinical player that looks for short passes and can reliably beat players and absorb pressure but he lacks effectiveness. Doesn't get into the right positions often enough, his finishing lets him down, etc. Bellarabi is the polar opposite pretty much. Adli is a bit more.like Diaby but also still very fresh. I think overall they simply don't have these such stark ups and downs as for instance Diaby or Demirbay who can have a great game than followed by an atrocious one.But are Adli, Paulinho and Bellarabi consistent, reliable performers? The fact that the experienced players may fall behind them isn't necessarily a positive. Demirbay has started the first 12 games, the fact that he only played 10 minutes in the last game could mean something, or it could mean nothing.
And while he looks to be good in attack, Bakker is actually the player I was most confident about, because he already has quite an impressive resume, from giving away a penalty and breaking Lainer's ankle, to the vintage Wendell display against Augsburg, to allowing Meunier to look like a force against Dortmund, to giving away a free kick at the edge of the box (that lead to a goal) and collecting an early yellow card with a stupid kick against his opponent.
Regarding your second paragraph: It's not like you can crack a defense just with tactics, the more defensively your opponent's setup and the better they are organized the more individual quality or luck you need. It's possible that Seoane can do more, but the fact that Leverkusen's players in some matches also seemed to struggle to play out clear counter attacks (and not at all for a lack of pace) and that CM is a bit of an issue (Demirbay inconsistent, Andrich limited) suggests that there is an issue with individual quality.
On the other hand mistakes that cost points are remembered more clearly and if your games stay close-ish in score, then each mistake weighs worse. So there is probably some truth to that the image of defenders is suffering from the consistency of the attack.
Regarding xG: according to understat Leverkusen are overperforming their's by nine goals, three of which were own goals and thus definitely just dumb luck. If you want to find out whether the models are undervaluing them it might be worth taking a look at the big overperformers, who are Schick, Diaby and Wirtz:
If I remember correctly Diaby often got to the end of counter attacks and in general I often feel like xG models are undervaluing the clearest of chances (that are often a result of counters) a bit, so maybe that's where a part of his personal overperformance comes from.
And you probably can't crack a defense through tactics alone but our approach against low blocks has been especially uninspired if you ask me. It is generally possible to create superiorities in certain areas and implement patterns of play that get players in positions in which they can play out their strengths. What changed so far under Seoane compared to Bosz is that we take more risks to play vertical. That's creating lots of chances when the opponent commits to attacks but if not our attacking approach looks improvised. Also, as you mentioned, we feck up many counter situations in comical fashion and if those are our primary attacking plan I expect the team to play them to the end in their sleep.
Regarding the xG bit about counters: That surely is a favtor. But personally I also think that we had some pretty great finishing as well.
