Yea but..you can't really use that instance as an example. Barry was trying to be careful and slow Linda's fall. While Thawne gave Firestorm a Team Rocket send off.
Yes Thawne used one hand to send someone flying while Barry used two in order to slow someone down, but while one is trying to harm his opponent, the other is trying to be careful and save his friend. So..it's not really fair to compare the two incidents when the motivations behind the two character's performances are very different.
I mean you have a point to be certain. But when one was used for combat against a metahuman while the other was used to save a normal human friend, you can't really compare the two. Barry could have just been using both of his arms in order to be careful by generating a wind of bigger size, yet less force than what Thawne used in order to protect his friend.