Sounds like a fair book to purchase.
Pretty sad that the Mass combat rules won't be in. I was really looking forward to those. Ah well... maybe next time.
As a point of perspective, I don't totally know who Xanathar is, other than a beholder in charge of a thieves guild apparently, and this was all learned from this thread. Frankly, that he is part of some FR lore will factor exactly 0% into my decision to by this book. I find it pretty weird that someone would get hung up on something like that. It has to be titled something, may as well be that. Probably better than what I would come up with.
Just my 2 cp.