Just so that I understand, will the team at Steam tell you what needs to be included based on their review of the release candidate? Or will they get that info from users after release somehow?
I’m currently checking the Recommended Specifications for UE4 and it has a list of all the things that their prerequisites installer will include. It mentions at the bottom that Xinput, X3DAudio and XAudio are very important as they’re not included in the standard installation of DirectX. So I’m just wondering if the DirectX June 2010 option on Steamworks includes those.
I bet you’re right that by checking DirectX and Visual C++ 2015 it is highly likely that everything will work perfectly (and certainly worked for your title). But to be completely certain, it’s worth considering including the Prerequisites installer and using a Steamworks build script that runs it. The only downside to that being that it takes a bit of time to install, and will ask if you want to uninstall if you have already installed it (which may cause some confusion to users).