I don’t see anything wrong with this squad and they can still fo wondrous things also this season. Adding more senior players to the team will really help them but I don’t think it’s a necessity now that the league have started and they started on a good course. Bayern Leverkusen still remains one of the strong contender for the Bundesliga title this season and without putting that great performance together, they will not be able to keep that consistency of wining the league again. Many clubs should fear them but i don’t think they’ll get it easier as they did last season. The league just started but they can’t keep the unbeaten streak this season after losing their most recent match, that shows how tough this season is going to be for them.
Talking about adding more senior players, is it by age or by experience, I don't know which amongst the both you mean but if it's by agree then I can assure you it's not going to help them well enough as you may rather be putting, where they will get the most helpful would be with young players, I even think it's much better maintaining the team as it was last season that they got all they did vet than trying to remodel the team and end up loosing vital players or scattering the pattern that has already been created. They can do much better with their patterns than they would with the introduction of newer faces who will need more time to adapt.