I live in Sicily, Italy since nearly a year ago and my friend who supports Napoli says he's an unusually cerebral defender. Always looks like he's calculating. They say he's intelligent. That's high praise in my opinion given how brutal I've found Italians to be in regards to their players. They also say he's fantastic on the ball in terms of passing. He rarely makes mistakes, but if they happen, they're normally fair gambles when you gotta put the team on your back...what I took from it is that he's not rash a la Otamendi.
I think most of us agree Laporte is also intelligent. They both speak French. I know Pep wants the players to speak in English, but as we've seen with the hispanophone contingent, that's not always the case on the pitch. When they gotta communicate something super critical or instinctive while defending in the Prem or Europe, it'll probably be in French and most attackers won't know what they're organizing between each other. Everyone understands English in football. That could be a tiny advantage.
Two smart defenders who have good timing, good technically, put their bodies on the line, have a burning desire to win. Fuck. This could be something special.
Are there other defenders who could give us more years than Koulibaly for a comparable or cheaper price and be just as successful. Of course. So why not go for them? One small reason tells me, Koulibaly is the better gamble. I probably know more stupid, or bang average people compared to the amount of genuinely smart people. Same applies to football. Koulibaly has shown he can adapt to a manager whose basics of positional play are highly situational like Sarri's tactics, consisting of hundreds of situations and what-if scenarios (ie: when the teams look like this, you need to be here, or do this...) This shows a guy like Koulibaly could have a propensity to learn Pep's tactics faster than the 21 year kid, who's still perfecting the art of timing a last ditch tackle and still learning the composure of not shitting your pants when he's one-on-one with you in the 93rd minute.