A Tank Commander wields a decent amount of power, but still has to answer to their CO. While they sit low on the hierarchy of the military, they are several ranks above other soldiers. At the minimum rank of Staff Sergeant, they have five ranks of soldiers below them.
In addition, they have complete command of their tank and their crew. While they have to answer to their Platoon Leader, they are in control of what goes on inside their tank. They can also park wherever they want and don't have to worry about a ticket. Don't try to valet park, though. You'll get funny looks.
There's also the very physical power of commanding an armored vehicle. Driving a 70-ton piece of metal that can destroy buildings, a Tank Commander is probably the closest real life equivalent to the Hulk. Minus the green skin, of course.