Tadese wasn't a better 10,000m than Gebrselassie or Bekele, no.
But the situations aren't comparable. Each 10,000m is one race. There's no stage-upon-stage-of-consecutive 10,000m. Often the riders who went on these long mountain raids were going on them NOT because the others were better climbers (we are talking about climbers here), but because the others were better GC riders. But we're not saying "who was the best GC rider of all time?", we're saying "who was the best climber?". Different questions.
To whit:
By the time the Tour got to the mountains in the Armstrong era, we'd usually had a prologue and either a TTT or an ITT. The strength of Armstrong in the chrono meant that he would usually be ahead of his GC competitors. And there would be an ITT coming up. As a result, the better climbers (if there were any) HAD TO attack from a way out, because if they didn't leave Lance behind, he was already beating them. And they had to take as much time as possible as he would beat them in the final chrono too. What this meant was that they HAD TO attack, whether they felt good or not. And with the strength of his team and his own quality as a rider, Lance was able to either settle in if he didn't feel great, and let them tire themselves out, or, if he felt good, go and take more time, because they HAD TO go with him because they couldn't lose more time - hence they'd go into the red and blow themselves up. Fuente's day after day 100km multiple pass solo breaks in the '74 Giro weren't a stylistic choice, they were his only way to win after he lost time into Sanremo - because climbing was the only area he held an advantage. It wasn't Tadese going from far, it was more like a triathlete with a slow run time going hell for leather in the cycling to try and build up enough of a lead to defend.
Both the GC riders who were in the position to let these people go from afar, and then hunt them down, and those specialist climbers who had to go from afar because they were lacking in another aspect of their GC armoury, belong in a discussion of best climbers.