I'm having the same experience with my f/2.8 II (and 70-200 f/2.8 II). Those lenses combined with my 5D MkIII have made my f/1.2, 1.4, and 2 (other than the 85 f/1.2 II) collect a lot of dust I'm seriously considering selling my 24, 35, 50, and 135, which I couldn't even begin to imagine not too long ago. I'd like to thank the OP for this one
Unless you're shooting events (i.e. very low light where you'd be at f/2.8, 1/60s, and ISO 6400+), sports (to stop motion), need really shallow DOF, or require lower distortion (only real weakness of the 24-70 f/2.8 II IMHO), the 24-70 f/2.8 II will be your best bet.
- you and the people who replied made me realize how little I use my primes. I've decided to sell my 35 f/1.4, 50 f/1.2, 135 f/2, and 400 f/5.6 to fund a 300mm f/2.8. I would love the 200-400, but the price is insane, I have both mkIII teleconverters, and don't shoot in Africa or the desert...
I'm holding onto my 24 f/1.4 - it's my 'desert island' lens - my FAVORITE focal length, and my walkaround lens of lenses. The 24-70 II may
kill it someday, too...but it hasn't yet...
I'm also keeping my 85 f/1.2. After buying it earlier this year, I realize that they hype around this lens is way understated. It's insanely good and killed the 50 f/1.2 off for me.
Just my personal two cents, many people prefer the 35 to the 24, 50 to the 85, etc., etc.