I think Arsenal doesn't have to make a major overhaul to become champions because they already have a pretty solid squad and a good coach. At most, they only need to sign a few players who are really needed and don't have to make changes on a large scale. Arsenal's real problem is that they still don't have the winning mentality that Man City and Real Madrid currently have, and I think if on several occasions they can reach the final, it will form that necessary mentality on its own.
Arsenal are not missing out on anything not to be a major contender of the champions league just like Manchester City and Real Madrid have been over the years now. Arsenal are a great team and they have all it takes to win any trophy now. Just like you’ve mentioned, they just lack that winning mentality and that is what have caused them to not have win any trophy for themself till date despite the great performance they pull up every season. If they can have that winning mentality and their mind set at making sure that they get what they want by all means, they can win a trophy in the next season. I have so much believe in them but they always disappointed towards the end of the season.
I think this is the only fact I have seen about Arsenal so far. They are really good and the squad is very strong, but I think the luck to win is not always by their side, and also, at the end of any season, they get slack; they don’t perform as they start the season; if not, Arsenal always starts all the seasons with great performances that no team can come near them that will give them any pressure by any side, but they always get problems when the season comes to an end. If not, if we are to talk about squads, the Arsenal squad is full and can win any trophies, but luck is not by their side, so I think they need to work harder to get things done for themselves because I believe they can do it.