its unfair to talk about the development time it take. to become faster you need multiple man, couple of high end computers and a large asset base and chunks of premade code(blueprints which you can reuse and edit. they have it all at DTG , even from TSC time there are models available which are retextureable. as 3th party dev you need to grow , and time by time it will go faster.
Maybe its better to hold more work under the radar and show something when DTG set a fixed release date.
But you are right that there are some things missing which are even not difficult, in my eyes some parts with weak texture work, no proper heightmaps which pump out the ballast. The ballast is atleast one part that need to look similar , or close or better than DTG.
to clean and simple texture work in the 628, dirt which reflects lights opposite( fair to say actually i seen this also at DTG work) . this texture parts doesnt take months to get right, this are hour task, i proof it on release day on the DTG forum with screenshots. i show visual proof that it can be done in short time. in that time on unity, but no problem in unreal to. Personally some parts can use more Substance painter, Quixel, Photoshop love. and yes and some skills.
The route is nice, complete new world and i do not say, its bad or the best. Make it the best is for every person different.