LOL, ... upon reading that quote, I just flashed on the saying: The straw that broke the camel's back. (or the 1.65 oz in this case) ... Bob didn't mean it that way, but I just love BPL & the quote above, one of the many reasons why I paid my money to be here :-) By the way (a friendly disclaimer), there is absolutely no disrespect intended within the following post:
So, where did this extra 1.65 oz straw come from? (or ... what does it take to exceed the heavy threshold?) Let's get to the 1.65 oz first: the OP's 4 liter gravity system added up to 217 gm which is 7.65 oz.
Bob's "current 2 liter gravity system weighs 7 ounces, including backup chemicals" Aquamira repackaged into smaller mini bottles are approx 1 oz for both (depending on how mini is mini, could be less than an ounce for both). So for a more apples to apples comparison, let's call the weight of Bob's current system to be at 6 oz (w/o the chem treatment). The rest is simple math to get to that 1.65 "incredibly heavy" ounce straw.
In my mind, the questions about the weight are this:
1.) Is that 1.65 oz worth having double the potential water carrying capacity? (After all, water IS heavy). But, the OP stated he only wants that capacity for convenience in camp ... so,
2.) Is that 1.65 oz worth it to the OP to have double the water capacity convenience in camp?
But the difference in the weight can be bigger -
Bob's 2 liter gravity system will soon go down to 4 ounces (w/o the weight of the chem backup) ... which will soon yield a difference of 3.65 oz between Bob's and the OP's system.
Glen's 2 liter gravity system (4 liter carry capacity) is 5.5 oz ... It is not clear if that total included adding "a piece of hose and a valve, and you get inline 2L filtering" but let's go ahead and assume it does, then that yields a difference of 2.15 oz between Glen's and the OP's system.
What does it take to exceed the heavy threshold?
For myself -
My aforementioned "heavy/elaborate" (= 4 liter) in-line gravity / hydration system is 5.7 oz. But my lightweight in-line system (= 2 liter) is 4.1 oz.
Coincidentally a 1.6 oz difference too.
While a much lighter solution would be to go with chem treatment, that's not what this thread is about. (I personally don't like the taste, and I'm willing to carry a Sawyer mini to avoid that, AND I'm willing to carrying a hydration hose for convenience).
So, for those treks compelling me to carry more water (OY!!) I'm personally willing to carry that extra 1.6 "incredibly heavy" ounce because I'll need that double capacity. Philmont for example(which my son & I went to last summer). Also if I'm not compelled to carry more water AND I'm NOT going solo, I MIGHT be willing to carry that extra 1.6 seemingly "incredibly heavy" ounce in weight for
..., wait for it .... just for the mere reason of campsite convenience :-D