I shoot those blue box 270win-130gr, they group the best in my rifle, I wouldn't hesitate to shoot a muley out to 500yds with that load.
No need for a super premium bullet when a good quality bullet is being used, ie I don't need a TSX for deer with my 270 when a core lokt will get the job done well.
I think using the correct bullet becomes much more important when you're marginalizing the cartridge/game being hunted. ie an elk with a 270 I'd much rather have a TSX than a blue box federals, but then again a blue box 300win.mag federal would be perfectly fine probably.
Magnum-itus does exist I think, but so does shooting tiny/dinky cartridges for game too big. Doesn't take a 300mag to kill a deer at 200yds, but I wouldn't go on a brown bear hunt with a 270 either.
Sometimes guys just have a favorite rifle/cartridge, my cousin would probably take his 375H&H on every future hunt if he could.