Your dad was 100% correct. And he could have easily said a 375H&H too, if other continents were involved, but the point he makes is not relevant to any gun lover. If you love hunting and the gun is just a tool for that purpose, I could not agree with him more. But if you are also a gun lover one gun regardless of caliber will be like a food connoisseur being told that all he ever needs to eat is chef's salad.

We want, therefor we need.

Slaves are allowed what they need.
Free men buy what they want.

I like guns more then I like cartridges I guess. I have learned in my 52 years of hunting in various states and countries and in hunting a large number of game animals of various sizes and weights, that what you shoot is less important then how well you shoot.
A rifle you LIKE is one you shoot for fun. Shooting for fun has a tendency to make you into a better marksman. Better marksmanship is the most weighty factor in success.

Generally I like powerful rifles, but I don't need real powerful rifles for any game under 2500 pounds. I just like them. I do have a 6.5X54 Mann/Scho (not much more power then a 30-30) that I intend to kill elk with this year. Why? Because I like it, and I shoot it well.

Bullets are more important then cartridge cases. Accuracy and penetration with enough cavitation is what we need.
The shape of the powder bottle is not as important as many seem to think.

But............ you're Dad was right if we look at "need".