jgsugden
Legend
Using concentration to cast *any* purely defensive spell you plan to maintain during combat is very questionable for any class, but is especially questionable when the biggest knock on the class is the weak damage output. When the defensive boon only applies to attacks versus AC, and not to save spells, it drops even more in utility. If there were a spell that said, "All melee and ranged attacks miss you, Duration 1 minute (concentration)", I don't think I would take it on a BS. It needs the offensive bump far more than a defensive bump.I don't really want to start another debate here on this point. Instead please refer to the probability distribution functions (the graphs) on page 35 of this thread http://www.enworld.org/forum/showthread.php?588010-Bladesinger-a-criticism-of-its-design/page35That should explain why Blur is worth your concentration slot. Not in every case, but in many cases.
Most BS I see running around rely upon Shield and Mirror Image to avoid AC attacks. Neither requires concentration, and both can be utilized (like blur) without sacrificing a full action in combat. The combination turns away AC attacks very well - including negating some crits. *Blur is more efficient than mirror image*, but as it does not require concentration, the difference is acceptable. They tend to use their concentration for either a primarily offensive boost (Haste), or utility (Improved Invisibility, Flight, etc...), or offensive spell (Banishment, Hypnotic Pattern, etc...).