They should just leave the work to people who are willing to do a great job. There should be no excuses when it comes to such kind of matters imo.
They create a product and we consume it. They had to release the PC version when it was ready. Today lots of game companies do the same thing unfortunately. Not only the games ported to PC but even the original ones (made for PC) have optimization problems. These companies demand more money every day with DLCs from users but they can't even release a completed product. Or they don't wanna, dunno.
I think GTA did good for the PC. And it was not that bad. It is just that there were some times when the GTA was not doing good on the graphics side which later changed for sure.
I dont think it was optimized. Then again we don't know what the developers do with the code. It may be possible.