It’s a bit of everything really. They spent all their money in the areas that needed strengthening the most. Players like Wijnaldum, VVD, Salah and Mane have turned out to be way better than anyone thought, I remember plenty of scoffing at the prices they paid for them but now they look like bargains. Trent looks like their best youth product since Gerrard and a lot of the pre-Klopp players have had their games elevated by him.
Klopp was the perfect fit for them, a passionate guy that a rabid fanbase could easily buy into. His style of play works exactly to the strength of every single player in the team.