I had the lens, when I had a 7D2, and also for potential use with my C100, so this is my feedback:
- the lens is heavy - as such, i would highly encourage you to go to a store, mount it on your camera, and see if it is something that you will use
- the 80D is a very useful video camera so, if this is in your calculations, I like the idea of IS lenses better
- while the lens is sharp, if is much better at F2 than at F1.8 so I never used it at F1.8 - it is even better, materially so, at F2.2 - so that is how I thought of this lens - a multiple, very heavy, 18-35 F2.2 set of Primes
- I own the Sigma 24-105 F4 OS lens, that I use on my full frame cameras, and that Sigma never, ever misses focus - I did not find that about the 18-35, at least on the 7D2 and its AF pts (if used in liveview it never missed or even on the A7Rii is never missed - but that wasn't true on the Canon using the Optical Viewfinder)
As such, given the weight, and not 100% consistent focus, and also without IS, I found this lens less useful that the excellent sharpness reviews would suggest.
I might offer another lens, that is almost never mentioned, as a great everyday, very useful crop lens, to pair with your Canon 70-200 - and that is the Tamron 17-70 F2.8-F4 OS Macro Lens. This lens doesn't get spoken about much, but I bought it for my brother in law for a christmas present one year, and he really likes it. The ability to zoom to 70mm, and its close focus macro ability, makes it very good for close-up portraits, the OS is excellent, the macro is useful when needed, and you get up to about 24mm? at F2.8 so it works for indoor family type events.
Hockey and wedding photographer. Favourite camera / lens combos: a 1DX II with a Tamron 45 1.8 VC, an A7Rii with a Canon 24-70F2.8L II, and a 5DSR with a Tamron 85 1.8 VC. Every lens I own I strongly recommend [Canon (35Lii, 100L Macro, 24-70F2.8ii, 70-200F2.8ii, 100-400Lii), Tamron (45 1.8, 85 1.8), Sigma 24-105]. If there are better lenses out there let me know because I haven't found them.