I took it to my local mechanic because of a humming in the passenger side tire when cruising. My mechanic tells me the ball bearing is starting to become defective and suggest replacing both front ball bearings which will be $500+.

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I have a 2015 Mazda 3 that has 33,000 miles on it (bought it CPO from the dealer at 28,000 miles, only driven 5k miles personally).

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Is it normal to have to replace both front ball bearings like this and not just the bearing on that wheel? He said it can be bad down the line if both sides' bearings aren't the same in terms of resistance. And mentioned that the rusty rottor will cause issues down the line, but I've only driven the car 5k, why would the rotor be so rusted it would need to be changed?

Plus he suggests changing the wheel's brake pad and rotor because of creeping rust, which would be $100 in parts, but labor is free because the brake/rotor will have to be removed anyway.