Welcome to our forum.
I am very aware of Hotsprings, their piping is no by pass, but that does not mean that water at those gallons per minute are not being pushed around the filters, the Ideal of no by pass plumbing is a good one and the play out of it in it's form now is better than not to.
Chas I think you forgeting that the pump has to return the water, so unless your pump has no return side hooked up, it has to pump it back up, I'm not sure, but that's what happens where I live
Let me put it in different terms, at the flow rate it is more the quality of filtering than the actual path of the water, if you take 2 equally dirty cars to a pull through car wash and ones goes through in neutral on their belt and the other goes through at 60mph which will come out cleaner. I bet there would be a big difference between the two, so like I said the Ideal is good, and it is better than not going through at all,
You guys go on about how much heat your covers that are usually 3 to 2 inch holds in, which in any insulated structure is (supossed) to be the most important, so why is it so crazy to believe that 4 to 5 inch of insulation all around the tub will not hold heat, in a sealed air space