To win the UCL you need a squad that is able to maintain its performance in every match. Arsenal must learn more from the success achieved by Real Madrid and Manchester City if they want to win this most prestigious championship. Arsenal still needs time to compete with Real Madrid or other big clubs, maybe it's true as you said, Arsenal should focus on the EPL first, when they are able to win the title, they can increase their target to the UCL.
What Real Madrid and Manchester City have done will be difficult for Arsenal to imitate. Real Madrid have built a very solid squad over the years and of course they also have a winning mentality in the UCL. Manchester City has good finances so club management can give Guardiola the freedom to choose any player he likes and form a solid squad. Both are the best in the UCL at the moment. Arsenal will take a long time to be able to compete with Madrid or City. But I think the EPL is more realistic. They had good form and the league and only bad luck made them fail to win. This season Arsenal will become even more solid and I hope they can maintain consistency in their game this season.
Arsenal are not ready to win the Champions League because they don't have the key players that can challenge Real Madrid and Manchester City yet, so they can just be struggling in the league with Manchester City in the league and try to get the title, but if it comes to the Champions League, they can't get the opportunity next season to win because I'm just seeing that Real Madrid can be the favorite of winning the title, with the players in the team and Guadiola will try his best and stop anyone in the UCL next season, because am thinking he will just play one season with Manchester City, but I don't real sure about the news. Let see who will get the opportunity and win the title or Ancelotti will do back to back for Real Madrid and win others title in the competition.
They have many clubs that I see they are more better than Arsenal in the league because I am sure Chelsea are strong and don't think they can get the opportunity they had last season will happen again Chelsea are signing better that will make them stronger in the league and compete with other clubs in the competition, arsenal can just be doing good anytime they start the league but at the end they will start performing weakly and making other clubs get opportunities on them and defeating them in the league and topping them. Even though Arsenal is currently at the top, I believe they will fall and should focus on the EPL. They may not have a chance in the UCL but anything is possible in the upcoming season.