I agree but with a slightly different twist. For reference, I've been shooting since the 1960's.A lot of people get bad advice, because the advisors assume that the advisee's have an infinite budget.
They need to get one, ONE pistol caliber that has sufficient killing power, and one, ONE rifle platform that can be ranged in to hit at 200+ yards. Then, cheap (hey, calibers matter, although with the run on ammo, bit late to the party) target ammo - hell even a .177 BB airgun and moving tennis balls - practice ammo, and train, train, train.
There are a lot of different missions for firearms. The practical self defense mission does indeed require simplification as much as possible unless the person is a full time professional operator. When shtf we revert to so-called "muscle memory", aka our training. I am a big fan of IDPA but not so much of race oriented shooting sports for that reason. Practice with what you carry, train for the real world as much as possible.
Functionality of one's defensive firearms should be as standardized as possible. Don't mix 1911s with Glocks, and don't mix ARs with AKs. Not when it comes to self defense.
Standardizing on calibers means never loading a 9 into a 40 with the resulting kaboom. When bugging out, everyone has the same caliber, which has immeasurable benefits. Ideally everyone is on the same platform, so there is magazine interchangeability.
Simplicity is a virtue when things get serious.
When the mission is fun, hell yeah explore whatever tickles your fancy.