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.