Code looks reasonable, do you think you could post some before/after? I'll check it out locally and play with it a bit later to see how this works out with different models.

Before: even at this level holes look bad:

After: much smaller hole diameter zoomed in:

With this change, people shouldn't be changing chord tolerance just to prevent octagons. When the holes look bad, any other curves will too, and changing tolerance should be the right thing to do. Also good for those smallish rounded corners.