The last thing I want is some 4th year undergrad or a Master's student who thinks they know better

They do know better. I've never heard of an undergrad TA in my department, but a first year Master's is still a student who had a high GPA and successfully entered graduate school in that particular field. A first year PhD student is someone who's done it twice, with even more experience and even higher pressures.

Automatically equating your low grade to "The TA doesn't have my intelligence" will get you nowhere, and arguing every low grade, will earn you a negative reputation in a department that will overthrow any high GPA. You'll learn this later in life.