Is there no way to keep my sceneries updated anymore without using GSX?
Almost all our latest sceneries require GSX.
It's clearly more efficient to have all common features, like Jetways, docking systems, marshallers, ground vehicles, which are the same across all sceneries, to be included in the GSX installer, which you download only once, rather than including the same stuff over and over in each scenery installer, making all of them way larger for no reasons, considering you need to run GSX anyway to operate jetways and docking systems in our sceneries.
Other developers calls this method a "common library", and for us it's GSX. There is a reason why it's entirely free to use at our airports. So yes, it's both free and a required download.