[romulus_ut3]

This is my understanding of the situation: Unless you're going to use something like Winhex to capture archive passwords during setup for educational purposes or whatever, extracting a Setup is not going to reveal the exact compression methods used. You can guesstimate what methods were used to an extent by simply running a setup executable, then go to run, type in "%temp%" without the inverted commas, look for the appropriate folder where the setup executable has extracted it's temporary assets, and examine the folder for relevant compression tools like srep.exe, precomp, msc, arc.ini etc. You'll then have an idea of which methods to use and the rest is trial and error.

You'll probably be able to achieve albeit better ratios compared to outdated conversions simply because there are some updated compressors available, but this will vastly differ from game to game. Some of these "conversions" were done using tools that extracts assets that're crammed into a single archive (like .sfar for Mass Effect 3 DLC) with the help of a third party tool, then inflated, then compressed with better ratios for achieving a reduced conversio size, and then the original asset archive is rebuilt during the extraction with lossless asset data, though this process changes the game's original asset archive's hash due to the rebuilding process despite carrying the same data, which is a very common phenomenon for RG's Unreal Engine based conversions. This process isn't going to reveal itself even if you could get access to the archive as you'll need to learn the usage of the third party tool as well to recompile the game asset archive that's done by the setup executable. Something like process explorer could be helpful in revealing the command line arguments used.