Spawning 1 and joining 1 raid a day, and MVPing each time, will earn you 70 regalia a month once regalia are added to the shop. So even farming casually like me, you could easily MLB a weapon in 2 months. The core drop rate from Experts is maybe 1 per 3 fights, and 1 per 5 from Normal? Add in the drops from the Catastrophe itself, and 1 spawn per day seems sustainable, especially if you start with a stockpile of 30 or so.