Nobody is talking about a magnum.
And a .243's ballistics are not superior to anything. I have a beautiful pre '64 Win heavy barrel varmint that's chambered in .243. I love the round. Best varmint cartridge ever made. That was one of my first guns I ever bought on my own, however I didn't buy it for a deer rifle.
But, there is really no good argument to choose .243 for a deer rifle. You are really at the top of the cartridge's capability loaded with 100 gainers. To me that's a very poor choice over 7mm-08, 6.5 Creed, .308, etc.
My shoulder is already hurting thinking about that 6.5 Creed recoil.
That would be true only if you buy your ammo at Walmart and prefer it in blue boxes.
https://www.youtube.com/watch?v=hY0w1c-gf18Why do you think she isn't shooting a Corelokt?