You ask very silly questions.
The answer is obvious. At the time they were the two strongest force users in the galaxy, and their midichlorian counts were also 2 of the highest.
Did you seem to forget this movie was made in 2003-2004? Lucas maxed out what he could with the CGI back then.
Watching them battle with force lightning and force shield the entire duration of their fight would not have been interesting. Because it's counter this, counter that. A lightsaber fight was a true test of a warrior.
Their fight was a perfect balance of force usage and lightsaber dueling.
And Yoda barely walking around doesn't prove he isn't strong with the force. Physically, Palpatine was severely damaged from Windu bouncing force lightning. But his mastery and knowledge of the force and the dark side continued to allow him to be extremely powerful.
Yoda was 900 years old. And you have to remember him and Obi-Wan were in exile each for 30 plus years. They hadn't used their peak powers in over 30 years, which was why Obi-Wan in ANH was slow and weak and Yoda was brittle and weak.