They need three experienced players to help them realize the club's success and achieve trophies, the players they have are indeed good but lack mentality. There is no need to make major changes because the squad that Arsenal has is already good, they just need to find some experienced players to make their mentality better. Mentality will be formed when they have players who are experienced enough in dealing with pressure.
It will take time for Arsenal to achieve what Man City has achieved and they will get that experience if they are able to maintain consistency in playing. In the Champions League, experience and mentality are very much needed because the competition is much tighter with several representatives from the existing leagues. Arteta must build this squad to be more ready to deal with pressure and they must try to find the right momentum.
Arsenal's style of play is very unified, they have succeeded in carrying out a style of play that is interesting to watch. Yes, you are right, Arsenal strength is very strong and they only need the mentality to become champions. Moreover, the Champions League is certainly very difficult to become champion because you have to compete with teams from other leagues where they are much stronger and have a winning mentality like Real Madrid.
For this reason, Arsenal needs time to become the strongest in the Champions League and succeed in winning the UCL trophy. Arteta only needs support from the players because the existing players are capable enough to carry prestigious titles. Many people think that Arsenal needs a new striker and maybe Arteta has already thought about it.