It is absolutely the case that drivers contain code to fix errors or optimize away mistakes made in top tier games. This is well-known and often can be demonstrated by renaming the game binary or making other changes. Sometimes this happens with the blessing of the game company, and sometimes it doesn't.
Or, sometimes GPU folks will send a team over to help the game studios fix performance issues during their development.
There are some studios who push the envelope and make beautifully optimized games. There are many, many more who ineptly cobble together components and make something that runs well-enough.
So it might actually be a good business strategy to just focus on building a popular game, and outsource optimization to the graphics card companies for free?
Or, sometimes GPU folks will send a team over to help the game studios fix performance issues during their development.
There are some studios who push the envelope and make beautifully optimized games. There are many, many more who ineptly cobble together components and make something that runs well-enough.