It is indeed risky spending money on a proven player (he has also done it in the CL as well as The Bundesliga, and let's not forget that he happens to possess a WC winner's medal as well), but not so much of a risk to waste funds on Zaza, or close to 40 million Dybala. All of them are unproven.
This guy is worth the investment as there is a lot of upside to his game, he is explosive and dynamic, and still very young. The whole injury prone thing is BS; he had one serious injury, and that is about it. Is he currently worth 30+ million? Most probably not (potentially, he could be worth 50 or 60). However, prices are inflated, and Zaza wasn't worth what we paid for him, nor was Dybala for that matter. Perhaps in a couple of years Dybala will be worth double, but he is just as much of a risk at this point as Draxler is.