To be fair, in that video of Ark he appears to have all shadows/lighting turned off which obviously makes it look dated. But also take into consideration that Ark has a much larger view distance, more varied terrain, and much denser wildlife than The Forest. I’m pretty sure the world size of Ark is quite a bit larger as well, but can’t find any official stats for The Forest. Ark’s visual style is kind of ‘meh’, where The Forest does pretty well, but that’s not really the engines fault.
The Forest has also been in development at least a year longer, and not even that long ago looked and ran pretty badly. I remember watching a stream of it where the guy streaming (with a beast of a computer) was still dropping down to single digit FPS at points, and he and his co-op buddy couldn’t even see each-other on the server. 