The PL is the most difficult league in the world and Arteta has played a huge part in Arsenal's rise. Arsenal have finished 2nd 4 times in the last 20 years and Arteta has done it 3 times. To say he hasn't brought success would be unfair. It's just not enough for the title.
And in the CL, Arteta also managed to get them in again and even made it to the quarter-finals, where they also lost very narrowly to a strong Bayern. So I think he's a successful coach at Arsenal!
Mikel Arteta have been leaning on his managerial role at the Emirates Stadium. He's given every he has and have become one the solid pillars in the club. Who doesn't think Mikel Arteta deserves his flowers? I think everything about Arsenal is just time and it's not yet time for Gunners to start reaping the good things they've labored hard for.
Secondly, the English Premier League is not some random easy League where one can easily win trophies without having to show workings and evidence. We know alot have happen in this EPL and how consistent most of these clubs have been without lifting a trophy. Time will tell.