To be honest I gave the 1st round to Benson, the second was even & Edgar swept the remaining 3 rounds.
You're way overstating it. IMO, Henderson won the 1st fight 3-2, and the last one could either have been 3-2 Edgar or 3-2 Henderson, was close as hell. I don't think you're factoring impact/damage into your scoring at all. A light pitty-pat grazing punch that a guy hardly notices does not carry the same weight in scoring as a clean, flush, hard strike that evokes a reaction does.
If you try hard enough you could find reasons to give him 9 rounds. Edgar's main weapons at LW are his unparalleled speed and recovery ability. Put that together with decent punching power and good wrestling skills, and you have an excellent fighter. That being said, I personally prefer a fighter like Benson for a champion than Frankie. I am not sure how he will do at FW, though, as guys at that weight are faster than LW fighters. Really looking forward to the Aldo fight.