The problems of inequality go well beyond living standards. E.g. political control in a very unequal society gets concentrated in a few people.
Especially the failures to replicate.
2. From Wikipedia it appears they responded to all the substantial criticism. It also mentions an independent study largely agreeing with the results.
3. This is one book amongst a mountain of research, and there are problems with inequality that go beyond those the book mentions.
It is indeed noble that the authors responded to the criticism, but unlike what Wikipedia seems to imply, they didn't manage to rescue their argument.
See https://marginalrevolution.com/marginalrevolution/2019/03/th... from another comment.