Auto Tone doesn't process bracketed photos to the same final exposure

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I did a quickie experiment with 9 bracketed photos with 0.7 EV increment and observed similar behavior of Auto Settings -- the Auto-adjusted images didn't come close to having similar effective exposures:

The original 9 photos had exposure values ranging from 0.65 to 5.56, while the Auto-adjusted photos had effective exposure values ranging from 1.36 to 3.36.

When you understand how Auto Settings works, there's no reason to expect that it would produce outputs with similar effective exposures. Auto Settings uses a machine-learned algorithm ("AI") that was constructed from a training set of thousands of photos that were adjusted by many "expert" photographers to their particular tastes. There's no particular reason to think that the collective tastes of those photographers would tend to adjust the bracketed photos to have the same effective exposure values. It may be that the photos presented to those photographers were not particularly over- or under-exposed, or it may be that the "expert" photographers tended to preserve the dark appearance of dark photos and the light appearance of light photos.

As Johan indicated, the command Photo > Develop Settings > Match Total Exposures will adjust all the selected photos to have the same effective exposure as the most-selected photo:

I assume that is done on purpose. If you clearly underexposed the images, then Lightroom takes this into account. Apparently you wanted a darker image. Have you tried 'Match Total Exposures'? That should do what you expect.