" He quickly dismissed this idea, stating that Christian values are the foundation for this country and, as a result, should not be changed."

The entire argument is absurd, as it implies that the removal of the phrase from the pledge would somehow change or eliminate a persons values. Last I checked, those values existed prior to the 1950's when the phrase was added to the pledge in the first place. Removing the phrase does not remove a persons values.

"He also believed that "one nation under God" applied to religions other than Christianity, and didn't assert a bias towards Christianity. "

But it does assert a bias towards the Abrahamic god. As you stated, the singular word "god" eliminates all religions that have no god or multiple gods, and leaves Islam, Christianity, and Judaism as the only applicable religions. Since all three worship the same god, it does in fact create a bias. It's a desperate, false argument.

The problem is, that the U.S. government cannot endorse any religion. "One Nation Under God" clearly endorses a specific religion, as it is more than apparent that the phrase was added referring to Christianity. At the very least, it is endorsing a specific god.