We don't use Light Shot or Trifurcate in BRs (except for applying Defense Down, but we don't do that either, since it is really only observably beneficial when used before a perfect 8-person staggered BR).
I don't know whom you're referring to when you mention Bloodletter-spamming groups of Archers, but that's not something I recommend in my guide, nor is it something I practice.
Light Shot delay is dependent entirely on your bow delay (4.0s for Crab Bow); the displayed cooldown is a known bug (see Current Known Issues on Lodestone).
The 8 second delay for a basic BR that does not take advantage of the bulk of actual BR benefits is 8 seconds of DPS uptime taken away from every single participating player. Let me know how long it takes you to do a proper BR. All magic and weaponskills must be from a different class than the magic or weaponskill directly preceding it in order to really take advantage of a BR.
Again, I fully encourage you to try Deepvoid Slave with as many controlled factors as possible, with BRs and without BRs. Beyond that, I don't think I'm going to convince you of the efficacy of unadulterated DPS uptime, nor are you going to convince those of us who hold contrary beliefs to you that BRs are, in fact, the bee's knees.