This whole Infused on the Back Bar and something else on the front bar means you have to swap weapons every 5 seconds to keep up the Weapon Damage Buff. I know there are players who swap like the dickens, I am not one of them. I am sure I am leaving some DPS on the killing floor, but it can't be all that much in the scheme of things.
I put infused on both sticks, with a Weapon Damage glyph, and then it does not matter when I swap bars.
You're not seeing this correctly.
Even though infused reduces the cooldown to 5s, doesn't mean you must swap every 5s. A 9s cooldown on the other hand is way too long. You will probably swap every 7s though.