Taking the facts and arguments presented together, it appears to be clear that no macroevolution is happening in “Darwin’s finches.”
The authors offer a selectionist explanation, which is nevertheless uncertain. Note the repeated use of the subjunctive.
This is by no means an all-or-nothing selection (as the impression is sometimes given). Rather, the alleles are retained.
They are not, per the National Academy of Sciences, a “particularly convincing example for speciation.”
How could the authors suddenly do this? Some of the following points may be considered.