While it is true that Messi had the best season in terms of goals (Both in Domestic and European Football) and is without a doubt still one of the 2 best players in world football, I don't see why Messi deserves to win it over VVD. Especially when while Messi won Laliga with a side that is clearly more talented than Liverpool on paper (in reality though, its a very different story), VVD dragged a side that featured Mingolet, Moreno, Lovern, Matip, Cylne, Henderson, Lallana, Sturridge & Origi into a CL title (a CL Final apparance before that) as well as being a stupid Lovern mistake away from winning the PL while a Messi-led Barcelona bottled it in the both the CL Semi-Finals and the Copa Del Rey Final (despite pretty much dominating the competition for the last 5 years or so).
So while Messi is clearly the better player than VVD, Van Dijk has clearly had the bigger impact in terms of contributing to his teams success as the last 2 seasons have shown. Certainly Liverpool would not be doing as well as they have done recently had they stuck to a Lovern-Matip CB partnership...