I think you're right, Lydia, about Barnabas and Angelique. I think A did change to some extent, though, in some way that would have made things interesting later, if explored, and not just ignored.
My concern with Desmond destroying the staircase is that he might retroactively undo everything B&J did. I think there's some key point, maybe not this moment when Desmond has his axe out, when if the Stairway were tampered with, all the events we've seen unfold would collapse and un-happen. I see the Stairway as a much more precarious phenomenon than you do. It's all about "physical space" and getting all the dimensions exactly right, so if you change the Stairway even a little, it might become just a staircase.
I was thinking that maybe Desmond's act might result in B,J,&E not being able to travel in time any farther forward than the few hours it took Desmond to chop away.
Anyway, really, I'm starting to think that the Stairway was responsible for the "temporal bubble" that this sort-of alternate 1995-1970-1840 existed in, and that once Desmond chopped it up, the bubble popped, and things went back to the way they'd been "before". So, B&J's actions in the "past" didn't save Liz and Collinwood, but rather Desmond's chopping.
And now we, like Trask, are trapped in parallel time, and the series, like Trask, will die there.
You're right! Good point!
Unfortunately, a lot of us do feel that sense of tiredness you describe, but
because of 1841PT, and if things had ended with 1840RT, at least there would have been a sort of conclusion, with the present's happy ending, and some satisfying concluding episodes with good writing for 1840RT. I think PT1841 is satisfying for DS fans who are more soap-inclined (or who enjoy those sweeping epic etc. romantic novels) than horror-inclined, and that wouldn't be me. I like romance worked in amongst the other aspects, like horror, not stared at point-blank... I can tell 1841PT is well done, I noticed that finally last time around, but it's such a different show that the horror music is out of place.