Sidious only had to be a little more powerful than Dooku to keep him in place.. He didnt have to be Massively more powerful and didnt even need to have superior lightsaber skills... Just as long as Dooku Knew that his Master was more powerful...
I believe Dooku did want Obi-Wans help to overthrow Sidious.. I believe he turned to the Dark Side becuase he knew how corrupt the Republic was, and was probably one of those Darksiders who thought they were doing the Right thing... but thats just my opinion.
Dookus lightning is most probably not as powerful as Sidious's... As Sidious is bound to have greater Force powers.. However this does not make Dookus lightning weak.. Remember the clone wars cartoons.. He knocked out Asajj Ventress in 2 seconds flat with his Force lightning while she was carrying 2 ignited lightsabers!!
Also just becuase Mace took Sidious does not mean hed take Dooku. Sidoius was quiet in their fight, and fights with BOTH hands on his lightsaber. Dooku would be talking to Mace in a fight with him, psychologically intimidating him.
Also he keeps a hand free to do a Force move with, or use Force Lightning, while simultaneously Lightsaber Clashing.. Its quite impressive really. His lightsaber handle has is curved for a more firm grip so he comfrtorbly fights with one hand.. Also his Form 2 technique helps with its parrying and minimum effort involved.
Anyway back to Mace vs. Obi-Wan... Mace isnt Dooku.. He doesnt keep a hand free to use an elegant Force move or use Force Lightning while simultaneously lightsaber clashing... So Mace wnt be doing that to Obi-Wan.. Their fight will be decided by lightsaber clashing... Mace will win due to his unique mastery of Vapaad, but it will take him a long time due to Obi-Wans Mastery of Soresu. Soresu Masters defences are supposed to be impenetrable and are sed to be invincilble.. But im still being kind enough to give Mace the win here.