It would be a transformative work by the definitions contained in section 107 of the copyright act and the case law based on what OP said he wanted to do.

It sounds like transformative to me.  A compilation of quotes from different books put together into a single book.

 And what's your point about fair use being a defense to infringement?  Of course it is.  An author of a work still has to know what fair use is if they are going to use other copyrighted material.  If they get sued for infringement, they better have their ducts in a row.

 

I am well aware of the four elements of fair use.

I have read many many copyright infringement law suit opinions over the years and I have a pretty good understand what fair use is.

I gave you my opinion based on the information OP provided.  That's all I gave.

Taking excerpts from a book and compiling them with additional commentary is transformative.

Which would be different then the purpose of the original work.

Substantially less than the original copyrighted work.

And would have no effect on the potential marked for the original work.

But since OP is going to use works in the public domain, this is all mute.