It seriously feels like the mod developer community sort of just lost interest in keeping their work up to date when Microsoft purposefully nerfed everything with version 1.13 - they were doing it as personal projects/labor of love and then they all seemed to lose interest. MCEdit has been garbage for ages now, Forge barely crawling back into existence, Schematica has been about to release an update for months now and on and on.
If the owner asked the builders to do the build for the owner and the builders agreed to do the work for the owner and agreed to relinquish all creative interest in the build then the work product belongs to the owner. This is exactly the analogy you gave at the beginning with the gentle reminder that the photographers for the company are "for the company" because they explicitly signed employment agreements or creative contracts relinquishing intellectual property rights. Absent said contracts (or chat logs or whatever in the case of MC build teams), the build would belong to the builder as far as intellectual property rights goes.
By the way, if they don't play the server then they are lying about having been the one to build it. Just saying...