The quoted figure would be for a situation with hospitals in perfect operational state.
So the Sweden reasoning is: we will stay within normal capacity even at peak, and everything will be ok.
If infection rate is actually slow, that may work, but it's not obvious this is true.
But you don't need to reach the level of people being denied treatment to be at an "overwhelming" level, where the hospitals are not operating at peak efficiency.
There have been many reports of hospitals not having masks, gowns and so on, or lacking ventilators or few people able to use them which need to be overworked. Many hospital workers have been infected, and hospitals had to switch to longer shifts.
It's just not business as usual.