Well it may be excessive or not depending on the situation.
I mean that is what it cost to attend college - the OP should have known that. If he chose not to save and postpone the payments, then no the loan isn’t excessive. I mean that is a personal choice how the OP wants to pay for it.
However, if the OP did not plan on paying any of it then that is a different discussion. He should have discussed that with his son up front and explained that he would have had to pay for his own education. In that case, he could have looked for schools where he could have gotten full scholarships or large merit offers. Obviously, he wouldn’t have applied ED to Cornell if he knew this.
So it is up to the OP to decide if he is going to pay for it or not.