My point about Rainier is that you can do it with your own equipment and planning and that would require more skill and still be cheaper than paying a team to take you to the peak of Everest. People are literally learning to climb 5.6 on Everest.

Sure, you can do Everest that way too (and then it is indeed very difficult) but that's not what we're talking about.

Altitude is certainly a challenge, but acclimatization takes out a lot of the difficulty. I actually had a harder time on Cotopaxi than on Chimborazo despite the altitude difference because I had 8 days of acclimatization in between.

It's also worth noting that a lot of Everest climbers have sherpas carry oxygen tanks up for them.