I don't think this game has been in development for four years, I think it was under two. I think it was made in ~18 - 24 months of development by a group of people inexperienced with the engine and framework they were working with.
Lets look at some facts.
- The UA Kickstarter concluded early March of 2015
- Underworld Overlord (their VR game in the UA universe) was released ~18 months after the KS, in December 2016 (link)
- So from the release of UOverlord to Nov 15th, you're looking at less than two years, making it ~23 months from the release of UO
I suspect that the KS funds and resulting press coverage were leveraged to develop a prototype of Underworld Overlord, their VR game, to pitch to publishers. See: Nightdive's SS1 as another example of this business model. These VR projects are usually heavily subsidized by the publisher, Google and partners in this (Otherside's) case, so that funding was used to start the real development of UA with anticipated Overlord sales also contributing resources. See: inXile's Mage Tale / BT4 development for another example of this business model. Of course, VR hasn't taken off, and the revenue that was anticipated, and thus funds budgeted, to support UA's development did not materialize.
So there you have it, probably two years-ish of underfunded development.
That being said, I'm sure they were following the inXile model and trying to develop assets and pipelines that were as applicable to both games as possible, and I'm sure there was some work done on UA during 2015 - 2016, but Overlord didn't make itself - it took man hours, attention and focus. And It was made by the Boston team.
As an addendum for the skeptical, when I say there wasn't four years devoted to development, I fully recognize that there were feature and art tests made, likely on a part-time basis by a subset of Otherside Boston. I believe there was a token amount of pre-production / thumb-twiddling happening for the first two years, well represented by them asking the community for help designing the lizard-man language, only to have the dialogue system dropped entirely. That's the process and product of dilettantes.