Michu has it right for PvP. BLMs may as well just forget about participating in the arena, because all you're going to be able to do is cast a spell every 30 seconds without interrupt (Surecast) or instantly every couple minutes (Swiftcast). Outside of that you're, what, a Scathe bot? Silly. If a team is going up against another with a BLM, it takes hardly any effort to keep someone on that BLM to ensure they very rarely get a cast off.