This comparison in this context either yields “it doesn’t really matter” or “there’s a slight advantage for the 6 creed.”
Given that reality, there’s nothing terribly wrong with buying a 243win, but there’s no reason to do so, while there ARE potential advantages to buying a 6 creed. Even if you dismiss the very slight powder cost savings, because it is slight, the simple fact it is notably easier to develop loads in 6 creed is reason enough for me. It’s not 6 of one, half a dozen of the other - it’s 7 of one.
The 243win has been my favorite cartridge for deer, hogs, coyotes, and midrange target shooting for over 20 years. With the advent of 6 creed, I’ve sold or converted all but one of my 243’s, and don’t expect I will ever buy another - and DO plan to convert my last 243win sooner than later. It takes nothing away from the 243win to say the 6 creed is better in multiple ways for this application.