Sometimes I think we could actually buy a horse (maybe not a stallion, but a good horse nevertheless) with the money we spend to buy three donkeys... I'm not referring specifically to De Paul, but it seems to me that we often get ourselves stuck in a loop consisting of two phases:
1) buy a goodish player who's done well enough in a smaller team in the hopes that he may be an improvement over the players we currently have
2) watch the newcomer perform more or less like the player he replaced because, in fact, he's on the same level as him
Rinse and repeat.
This small-time mindset is what made us sign Gagliardini for 30m and then Vecino for 25m, which has ultimately left us with two mediocre midfielders, when we could have spent the same sum on a single top player.
In saying that, I'm perfectly aware of the FFP constraints we still have to face. I also realise there are several clubs we just can't compete with from an economic point of view. However, I believe it would be better to spend big on a great player (the best we can afford) who can make the difference than to keep gambling on players who have still everything to prove (Gagliardini, Gabriel, Joao Mario, Keita, Politano, and the list goes on). Especially considering the fact that, even though Pierino occasionally hits the jackpot with his punts, his hit/miss ratio remains rather underwhelming.
That must be Rummenigge, although Palacio definitely ranks high in this particular list.