She's a strong bender, which I stated, she's just technically not the best technique wise. She's like a Street Fighter player that Hadokens their way through fights. Her physical prowess is the reason why she's so deadly. Aang wasn't the best earth, fire or water bender, but he was a master class airbender and it showed. Korra doesn't really seem like the best any bender in Korra, she's just the strongest bender. She's not even a better or at least more creative water bender than Ming Hua, but she'd probably brute force her way through that fight. She's like mid tier tops in her bending elements technique wise.
Pretty much this, honestly she would probably lose to any master bender one on one if they were using only a single bender. And not the chumps that the White Lotus call masters either.
Korra probably never had to learn to be creative with her abilities, restrictions force us to be creative. When she could bend 3 elements at 5. It pretty much prevented her from learning the ins and outs of the element like regular benders and Aang had to do.