or is this just a bunch of baloney?
No, averages are real, everything has an average. But it cannot be used to increase the accuracy.
For example, in every 18 spins,
on average there will be exactly six numbers from dozen 1, six numbers from dozen 2, six numbers from dozen 3. Or
on average there will be exactly 9 red numbers and 9 black numbers.
So after 9 spins and 7 black numbers, can you bet on red to catch up with the average? No you can't.
Sometimes in 18 spins you will see 12 blacks and 6 reds, then in the next 18 spins you will see 12 reds and 6 blacks. This is the variance of random. But the average will still be 9 for both colors.