Then everyone should just have a 12g, a .30-30, .22LR, and a .45-70. Boring!!
You musta forgot a bolt rifle in your line up, then I say, yes, complete.
I didn't say that is all one would ever need, however, with the 300BO, where it shines, is so limited, to me, it seems nearly pointless. My rifle calibers (center fire) are .223/5.56, .243, 7m-08 and 30-06. These calibers can do everything and more than the 300BO and more. The 300BO isn't nearly as capable as the others and will do only a fraction better in a very small niche use situation.
I would also imagine there are a handful of 300Blackout fanboys that pump up this cartridge because it has "blackout" in its name. It does sound tacticool at least.