As I said, it's about progress. If after 4 seasons we're still hovering in the same position and there's no sign that we're getting nearer to the top then fans will want a change. That's not to mean he'd have done a bad job. Discounting another Leicester scenario, we're still in a position now where Liverpool (or Arsenal) have 5 other sides that in any season could finish above them. All 6 sides can't qualify for the CL let alone finish 1st - you have to look a bit deeper and ask yourself whether things are improving and if not, will they in the future.
Why are you being so defensive?
If you read through my posts regarding Liverpool over the last 7 years or so you'll see I've been more critical of our club than anybody. Chopping and changing every 5 minutes most certainly isn't the answer but there's a huge jump from that to the situation at Arsenal. If Wenger had been at the club 2 seasons and there were signs that things were moving forwards then great. Can any Arsenal supporter say there's been progress at Arsenal in the past 10 years though? Looking from the outside I don't see it.
As I said, Arsenal haven't underperformed in any given season over those 10 years - they've always finished in the position they've supposed to be, give or take. The problem is that nothing is changing, there's no signs of progress and it's difficult to see if how things will improve under Wenger. If Arsenal fans are happy to finish between 5th-2nd every season, get to the last 16 of the CL and win a domestic cup every few years then fair enough but the growing unrest suggests they're not.
Two seasons ago you finished above Spurs but the general feeling was Spurs had the better season, why? It wasn't just because Spurs have fewer resources, it was because there was clear progress from Spurs. They were building a side and things were improving. Arsenal was the same old Arsenal, they'll threaten to challenge and then when it counts they'll fall away only to come back strong in the final weeks, when it's too little too late.
Apologies if it came across that way.
My point is two fold. Liverpool have been doing exactly what people are suggesting Arsenal do and it hasn't worked. I like Klopp a lot but he is erratic and I don't see Liverpool winning the PL or CL in the next 5 years.
Also maybe Arsenal and Liverpool are where we are because of forces outside of our control. Whatever nonsense is spouted about season ticket prices and how we've had or spent fortunes, we cannot compete financially with 3 of the other teams in the leagues (I have no idea about Liverpool's finances), no where near. Anyone saying Arsenal should be progressing I ask how, in light of the fact that some teams can spend on one or two players without breaking a sweat what our whole transfer budget is? Highest season ticket prices means nothing next to a Russian or Arab sugar daddy.