You are right that simply spending much of money does not guarantee great team building one takes more than just cash and it sounds like you believe Leverkusen is more focused on smart financial growth. Big news is that Erik ten Hag is now coaching Bayer Leverkusen which makes everyone wonder who he will sign first. Since his old club Manchester United is selling players this summer it is very likely he might try to bring some of those familiar faces to Leverkusen. He knows what these players can do they understand his tactics and they might be cheaper or easier to get which would help them fit into his new team faster.
In modern football money is very important because teams can buy quality players so they can support the success process achieved by the club, unless the team has academy players and they have the skills to change the competitive landscape in the League. Leverkusen are not one of the teams that are financially focused and maybe this team also does not have the big finances to make a long term project so what needs to be done is to use each player's sale to buy other players. Ten Hag's presence is expected to maintain what Xabi Alonso has done and even though it is difficult, they deserve to give the Dutch coach a chance.