@Ghostcrawler I hope you're not serious about Challenger being solo ONLY to reduce queue times
The exception is challenger, which is a necessary compromise to preserve reasonable queue times, not because challenger is somehow more pure and therefore deserves real solo.
It makes sense for Challenger to be solo but queue times shouldn't be the primary reason. Challenger rankings are used for scouting purposes and also supposed to objectively show who the best players are individually. When you mix both solo and duo, it can distort the rankings at this ELO almost as much as a 5 man would in Silver ELO. For example, if one ADC main only ranks when duoing with his favorite support, it's likely that an otherwise superior solo ADC wouldn't get as far on the Challenger ladder.
Having the Challenger ladder be solo is just more fair and logical. It allows direct comparisons between players since they all operate in the same environment. Even if there was no greater ease climbing duo it's still hard to isolate individual performance and adds ambiguity to the ranking. Is that ADC really amazing or is he just really good with this particular support etc.?
This kind of explains my point, althought it's a bit different subject.