While I personally feel that the spyglass isn't a good piloting tool, it's a great tool for engineers and gunners. However, having it be a piloting tool allows the other classes to bring it without limiting their own loadouts. It also makes that pilot tool slot useful for them, since it's the one tool of the pilot's (currently) they can use without being on the helm.
So while an omni-slot would be fine and dandy, taking the spyglass (and other possible future piloting items) from the pilot class and putting them there wouldn't really benefit the other classes much. Since there would be nothing left in the pilot items that they could make use of, making the pilot items useless and replaced by the omni-slot for them. In theory the pilot would benefit, since they generally don't bring utility items like the spyglass anyways. Having the omni-slot would allow them to do so without sacrificing other pilot items they could use for actual piloting.
tldr:
I agree with Crafeksterty