Can't do that then Castrum would become the best way to grind, right now it's about time neutral. You can get roughly 4 CT completed in an hour without BLU and CLL can be completed in about 25 minutes, factor in queue times neither is faster or slower than each other just one requires less focus until it eventually becomes available and then it's a lottery to get in.
It's when you take BLU that CT becomes the fastest way to grind but one person leaves you're stuck waiting to refill your premade.