snip

The builder is not playing it off. He is upset and consulted an
engineer (?) who hasn't looked at the foundation, but told the builder
it should be fine.

I think the above is the key...the builder isn't happy with it and is
willing to solve the problem. If he consults an engineer for the solution,
then you should be in good shape. Of course, you're free to hire your own
engineer...but realize that the builder is acting in very good faith to
resolve the problem. I might ask for the opinion of the engineer, in
writing (and possibly sealed) to have in my files for the house, just in
case, though.

P