GTA 4 was just like many multiplatform games of last gen, developed on a PC targeting console dev kits, so they were coding on the pc and running the code on a devkit. They then port the console version to the PC. GTA 4 ran like crap on everything, so the PC port wasn't as bad as people make it out to be since it never ran well in the first place. But ofc the PC port was hardly amazing either. But i was still playing it on the 360 for a while after the PC port was published so i have no experience of how bad it may have been originally.