It's hard to evaluate him from just looking at the numbers.
In his first season they won the title back from Twente, but finished with a lot less than points than that year before. They were in 4th when he took over in December and finished 1st, though. They of course sold Suarez that January and got tonked in the Europa League round of 16 (didn't advance in a CL group of death with Real and Milan, but that was with Jol in charge) by Spartak Moscow. Lost in the final of their league cup.
11-'12 they also won the league (96 goals scored), failed to get out of the groupstage again (Real and Lyon) and lost to the rags in the round of 32 (though they ran rings around them at OT).
This year they're ahead by the slimmest of margins in Eridivise and had nearly as bad of a CL run as we did (again, Real and Borussia). Steau knocked them out of the round of 32 easily.
In those years they've lost Suarez, Stecklenburg, Van der Wiel, Vertonghen,and for the most part replaced them with players already at the club (fits Txiki and Soriano's model of promoting from within).
So great in the league, indifferent in Cups, poor in Europe (tough groups every time but no success when dropping into Europa, either).
Haven't seen Ajax aside from our 2 games but perhaps like Laudrup he needs more seasoning before it's time to go to a club in England that wants to win 4 trophies a season.