Casting Iain Glen as Bruce Wayne in the second season of Titans could correct some of the series' biggest mistakes regarding how it handled Batman in season 1. In particular, having a strong actor in the role of Batman could do wonders in strengthening the subplot built around Dick Grayson and his internal torment over his role as Robin.
This conflict was a key part of Titans' first season, which saw Dick Grayson working as a police detective in Detroit, trying to put his life as Bruce Wayne's ward and Batman's sidekick behind him. As the season progressed, however, it became clear that Dick was suffering from some form of PTSD as a result of his working with Batman. Yet despite all of the attention paid to Dick's vigilante mentor, Titans told us far more about Bruce Wayne and Batman than it ever showed - and it told us very little.
It is understandable that Titans' showrunners would want to avoid Robin and the rest of the cast being caught in Batman's shadow. Indeed, Dick's entire emotional arc in season 1 is built around his trying to become his own man rather than the weapon Bruce Wayne turned him into, and escape from being forever attached to his mentor. Unfortunately, in trying to keep Batman from stealing the show, the writers only made him more conspicuous in his absence.
Titans went to comical extremes in trying to hint at Batman's existence without ever actually letting the audience see him as season 1 progressed. This culminated in the season finale, where we see Dick Grayson forced to bring down his foster father after Bruce crosses the line and becomes a crazed killer, in what was revealed to be a nightmare triggered by Trigon to awaken Dick's dark side. Until the very end, we only see Batman in silhouette or a fleeting glimpse of a distant caped figure. While this may have been meant to dehumanize Bruce and leave the audience seeing him as the monster he had become in Dick's head, all it really did was make it all the more obvious that Brenton Thwaites was facing off against a stuntman.
By casting an actor of Iain Glen's caliber as Bruce Wayne and allowing him to be seen, the audience can finally put a face to the name and begin to form an emotional bond with Batman's character, for good or for ill. Once the audience has something real to connect to rather than their projected image of what they think Batman should be, the emotional arc of the show's writing can fully impact the viewers. This can only serve to strengthen Titans' storyline in season 2 and make the show better.