Both you and @briandear are correct. On a sustained-alpine-climbing level, there are hundreds of routes/mountains harder than Everest. And to be sure, there are huge, difficult routes with thousands of vertical meters of sustained alpine climbing on 7000m+ peaks that are far beyond the Everest north and south normal routes and only attempted by the top 50 or 100 climbers on Earth.
But nonetheless, Everest is very hard no matter who you are. I disagree that Cotopaxi and Chimborazo have much do with the difficulty of Everest. These are mountains climbed in a single push from a medium-altitude camp, with only one or two hours spent above 6000m on Chimborazo, let alone 7000m. Trekkers in the Himalaya may sleep at higher altitudes than you ever would on Chimborazo. The hut you likely launched your summit bid on Cotopaxi from is not significantly higher than airport you fly in to in Lhasa to climb Everest from the north. Besides the far lower altitude, it's much easier to find a weather window for the 6-10 hour summit bid. I don't mean to downplay the challenge of the Andean volcanoes, but merely to tell you than the higher you go, it gets much, much harder. 6000m is only the beginning of "high altitude". I've climbed 6000m peaks in a weekend coming from sea level with one night of acclimatization. It's not the same by any measure.
Everest is an achievement by any route. No, it isn't the same as soloing huge routes in the Alaska Range like Colin Haley or Steve House, but that doesn't make it any easier.
I don't get your point about Rainier. Disappointment Cleaver on Rainier is a tourist route too, with no significant technical difficulties. Everest South Col is that plus a whole whack of other challenges.