Arsenal manager Mikel Arteta has been under intense pressure from fans and the media alike. The Gunners endured a disastrous defeat in the Europa League semi-final against eventual winners Villareal - against former manager Unai Emery no less - and failed to qualify for Europe for the first time in more than two decades.At the very least, calls for Arteta to be sacked have greatly intensified. Some reports say that Arsenal are considering former Juventus and Chelsea manager Maurizio Sarri as a potential replacement.Villarreal progress, as we are eliminated at the semi-final stage.🏆 #UEL— Arsenal (@Arsenal) May 6, 2021On that note, let's take a look at four reasons why Arsenal could be better off by letting Mikel Arteta go.#1 Mikel Arteta isn't a good fit at Arsenal2020 FA Cup Final - the undoubted high of Arteta's Arsenal managerial tenure.The Spaniard became Arsenal manager in December 2019, amidst much questioning by fans and media alike, given his severe inexperience.He was a capable assistant manager under Manchester City boss Pep Guardiola and was part of City's 2018 Premier League-winning and 2019 domestic treble set-up. With Arteta among their coaching personnel, City amassed 100 points in a season and became the first team to win the Premier League , FA Cup and League Cup in the same campaign.However, the Arsenal job - Arteta's first-ever managerial gig in football - may have come too soon for him. As a Gooner myself, I did not want him for this reason alone.Unai Emery had to go as he was not sorting out the defence as required, and results were not improving. But to expect a managerial novice like Arteta to transform fortunes was probably a bit of a reach.It was a highly peculiar decision to bring Arteta on board, one that wasn't likely to bear fruit. Except for a stunning FA Cup win in 2020 against Chelsea at Wembley - the club's 14th title in the oldest club competition in the world, there hasn't been much else to show.CONGRATULATIONS, @Arsenal 🙌#EmiratesFACup 2019-20 CHAMPIONS! pic.twitter.com/K61fQl388o— Emirates FA Cup (@EmiratesFACup) August 1, 2020Granted, the 1-0 Premier League win at Stamford Bridge this season against a Chelsea team that reached the FA Cup final and won the Champions League was pleasing. Many fans were expecting an easy Chelsea win, but Arteta made Arsenal 'park the bus' to the tee to get the win. However, that doesn't alter the perception that Arteta may not be the best fit at Arsenal in the long term.#2 Arsenal's defence remains a worryDavid Luiz has been hot and cold at Arsenal, but Arteta decided to extend his contract.Arsenal ended their 2020-21 Premier League season with the third-best defensive record. That is laudable, but stats can be misleading, and perceptions can often cloud realities.Nevertheless, Arsenal are far from having one of the best defences in the Premier League. Part of that is due to years of poor performances and having poor personnel. A few Arsenal defenders, such as David Luiz, are notoriously error-prone and inconsistent with their performances.Arsenal's defence has been poor for years and was a major factor in the angst held towards their long-term Arsene Wenger. The perception was that the Gunners have had a poor defensive structure, and many defensive gaffes have been due to weak off-the-ball work.Unai Emery didn't do much to correct that and neither has Arteta. It was a major reason for the Spaniard's eventual dismissal as well as poor results towards the end of his tenure.Arteta initially did get Arsenal working harder off the ball. That was exemplified in his first few games at the helm, where Arsenal narrowly lost to Chelsea 1-2 at the Emirates and beat Manchester United 2-0 at home.Good performances in the FA Cup in the semi-final (beating his old team Manchester City) and the final (against Chelsea) further added to that narrative. But that has turned out to be a false dawn.A primary reason for Arsenal's poor defensive displays is not just poor defenders but players who have a weak reading of the game and are susceptible to lapses in concentration at key moments.In all fairness to Arteta, most of these players were not signed by him. The likes of David Luiz, Rob Holding, Sead Kolasinac, Shodkran Mustafi and Hector Bellerin have all played under Emery, and a few did so under Wenger as well. But Arteta extending the contract of David Luiz, despite his erratic performances, portrayed the Spaniard in poor light.A week in the life of Arsenal Football Club 📅June 17David Luiz error leads to Man City opening the scoring 🤦‍♂️David Luiz concedes his fourth Premier League penalty of the season 🙄David Luiz is sent off 🔴June 24David Luiz signs new contract ✅ pic.twitter.com/kVM0kYJDku— Goal (@goal) June 24, 2020