I think if you go through every signing Wenger has made in the last decade or so, I'd say these guys were pretty high on the scale.
I can only really think of Cech, Sanchez and Ozil that clearly top them as signings, possibly Xhaka since people seemed to rate him (though if you were judging it in Summer 2016 then Mahrez trumps him) and maybe Podolski since he had a bit of profile and Arshavin too with that EL(UEFA cup?) campaign and Russia's Euros but beyond that I'm stumped.
You can't tell how players will work out as players obviously but as signings and hype, even good players that we'd heard of like Rosicky, Arteta, Mertesacker, Debuchy, Nasri, Chamberlain, Mustafi, Perez, Giroud weren't as highly regarded as these two IMO.
These are the kinds of signings we should have been making in between the Ozils and the Cechs.