Because he's a very pragmatic coach, he can get results in high profile games. I'll give him that. But I don't think he has what it takes to make a team perform over 38 games looking at that Liverpool side.
As far as player evaluation goes, I reckon he would want to have a big voice in that, I don't trust him at all. He bought so much carbage at Liverpool apart from 5 good transfers or so.
Maybe he can do with Arsenal the same as he did with Napoli. Solid, but anonymous seasons (although 5th with them in his second season is nothing to get excited about). I don't believe he can take Arsenal to the next level.