It seems that OpenRA requires Mono 4.6 with the version available in Lutris. The version available in GetDeb for Ubuntu 16.04 does not, which uses Ubuntu 16.04 Mono (version 4.2):
Version from GetDeb: 20170527-1~getdeb1
Version from Lutris: 20170527
Would it be possible to get a Mono 4.2 compatible version to support Ubuntu 16.04 without weird PPAs required?