A young team have always a potential to mess things up after everything looks great for some time. But this season is still a big progress for Arsenal as they finished as the 2nd in the standings and joined the Champions League finally too.
You could see it two ways I think. On the one hand Arteta did a great job simply because nobody expected Arsenal to be leading the table for so long and they played with a system and repeatedly delivered their best performances on the pitch. When everyone thought that this will end rather sooner than later, Arsenal kept going and I think Arteta did a great job there although it wasn't enough to beat Manchester City.
Ten Haag on the other hand had a difficult start into the season with lots of drama and then the danger that came with Ronaldo being turned into a substitute rather than a regular player. I thought that this could be a dangerous turning point for ten Haag when the team keeps losing several games in a row, but he overcame the trouble with solid decisions and also with consistency in his mindset and in his actions. Both deserved a good finish and also a good assessment for their performances as the managers.