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.
Reaching the final will take them a lot of sacrifice in order to get there. Arsenal has the needed squad to go as far as they want in the competition. All they need is that mentality as you’ve said. If they lack that, then they cannot go far in any competition they’ll be participating in. They’ve tried a lot of times in the domestic league to triumph, but I guess their mentality always falls when they’re close to winning it, could be that they are so sure they can win it at that point and then retard their performance. The champions league is a more tougher league than the premier league, in order to reach the final stage there, they need to exert more efforts to finish well in all matches.