It looks like there are several issues. The first one and the easy one to fix is that the gamma was not being applied, so I have passed that through the node now. The second problem is that when the environment is using the script node for it's texture the importance sampling doesn't do anything. This is where you are getting your hard shadows, etc. If you turn it off on a normal texture node it looks just like the script node. It's either something I'm not setting up correctly for the texture or there is a bug.
Linux Mint 19 x64 | Nvidia GTX 980 4GB (displays) RTX 2070 8GB| Intel I7 5820K 3.8 Ghz | 32Gb Memory | Nvidia Driver 410.66