True, but I would counter that 4K is still totally worth it. You capture at 4K, but after you edit, deliver at 1080P. The image will be cleaner and sharper than if you capture at 1080P and deliver at 1080P. Personally I see no reason to upload 4K to YouTube or Vimeo or any other website. But if you want the best possible 1080P image from a GoPro black, then capture at 4K/30 or 4K/24,, then downres it in post to 1080P. Just my opinion. One nice thing about down rezing a video image is that it naturally reduces noise in the dark areas.
As for 2.7K at 60fps. Thats a really good option too. You can still downscale that to 1080P for the web and you benefit from the 60fps smoothness. My only thing about 60fps is that I don't like it. I prefer lower frame rates that look more "cinematic". Unfortunately this means I have to be really careful about which ND filter I'm using and making sure I get the shutter and exposure just right. (because lower frame rate is more susceptible to jello/vibrations) But I'm rambling so I'll stop now.