The flipping method is mandatory on bypasses to bleed the air out. Coilovers you also have to cycle the ifp as well to bleed the hoses, and i also have a vacuum setup to assist with some funky shaped hoses and such BUT at the end of the day you are still submerging a piston assembly that has trapped air pockets in it. It takes awhile to pull the air fully out of the piston assembly and shim stacks, and once you get into the larger +3.5” shocks that timeline grows exponentially.
I don’t care if you are a backyard guy and just zipping through your shocks to get them back together and on the truck, what i do care about is the guys charging boatloads of cash for these services and they barely flip the shocks, pop the pistons in, and call it a day. Short of having bleed screws in the shocks to bleed off the air, i don’t think there really is a way to truly have 100% of the air removed from a shock. The goal is to remove as close to 100% oxygen as possible, and it is a lengthy process if done correctly.