I'm a big fan of Deathlands, but as has been pointed out multiple times here, there's a lot of BS in the books. You really just have to take it all with a grain of salt and enjoy the books as a form of entertainment, nothing more.
I mean, even if the world in the books was 200 or so years ahead of our own in terms of technology, there are some things that are simply too hard to believe - radiation lingering 100+ years after the nukes; likewise with changes to the weather system; horrific inbreeding that seems to occur within two generations; etc.
Mildred... yeah. A lot of fans don't seem to like her. I have no problem with her for the most part, but a lot of what you pointed out bugs me a bit. A lot of this can be tossed at the feet of LJ - for some reason, he overdeveloped this character, so now we're stuck with all that canon. *shrug* Don't know where you get her expertise with Indian affairs, though; AFAIK, Doc is the only one who knows anything about Indians, and he's spent time with them (he can speak a smattering of Apache or Sioux).
Ryan: This is more due to "multiple-author syndrome" than anything. Different authors bring their own visions to the series, so characters can change from book to book. You can't do much about it but grit your teeth and bear it.
Likewise, points 4 and 5. A new head editor took over in 2000; he decided that the series would become static - that all the books would be self-contained (except for short story arcs), and no changes would be made to the companions. This is because we have many authors writing for the series, and it would be difficult to coordinate all those authors to create a continuous storyline (before Mark pops in here, I'll note that he did it just fine in OL by having the other authors run their stuff by him first ). This would, of course, include adding/removing party members (which is why some people who join the party at the end of one book aren't there at the beginning of the next).
Thankfully, we're starting to see some things change - Dean's back, Doc has a new(er) LeMat, and the others are going to get new weapons as well. I doubt we'll see any continuity like before, but that's okay.