I have 4 and there's a lot of truth in what your dad said (sorry).
Your dad forgot about the ruddy car (lucky him from the generation whose children didn't even use seatbelts). See all the threads on here about fitting 3 seats across the back of an ordinary size car.
We just don't travel any more, lol, that's how we solved the hotel thing! All supposed to be at a London wedding today but only 2 went in the end due to tummy bug.
Speaking of which, Tummy bugs take forever to travel around the family.
Laundry is ceaseless and keeping organised becomes paramount.
Woman's career tends to die (mine did).
If you already have 2 of one flavour, and 3rd child turns out the other gender, a whole new set of costs present themselves.
But otoh, (sorry to be morbid), for me it would be less devastating if I lost one of them and had 2 or more left (as opposed to just one or none left).
And I like a busy family atmosphere, the fact that when I grow old the siblings will have more of each other to share the burden with of looking after me, we get some very family jokes and wit going, they keep each other company, they all become experts in negotiation.