Soren is much older that Picard, more experienced, and more desperate to win, Picard beat up Nausicaans and Klingons. The script called for Picard to lose the first time. Soran had a disruptor.
Watch it again, please. On the bridge, Picard had to use both hands and all of his strength aginst only the one arm of Soren to make him drop the disruptor. Soren hits Picard once and kicks him in the leg and Picard goes down. Picard pulls himself back up by using the handrails and Soren easily knocks him off the bridge. Kirk shows up and wins the fight. (Shatner is older than Stewart, but I don't know the Kirk vs. Picard age at this point).
Don't forget that Soren was not a human being. He is El-Aurian. Different races, different abilities.