I actually once recently read a theory somewhere and someone did in fact hold that almost everything except the campfire was a Kirk dream.......hey if it worked for them.........why not anyone else!
And you do have to show that the future is not set (to borrow from another franchise) but that some work was involved in making it and keeping it that way. This is why certain aspects of the new film don't phase me at all. There are a lot of ways to express these ideas overall.
In the case of DS9 yes they did do something similar (which I very much value and enjoy), but I would counter that they didn't do it by veering drastically away from the characters or the origins of the series premise. Here the DS9 story had it's seven full seasons to play out slowly and steadily (the War/Conflict storyline was ultimately played out over 5 whole years, not two hours) and DS9 started off as a darker take on the Star Trek universe anyway. This had allowed it to prime us for stories that took the characters (and the Federation) into far murkier water - with obviously some lighter episodes in there as well - therefore I would argue that it had more of the general tonal consistency for it's material choices.
For example, by the time that Sisko had to make his choice in 'In the Pale Moonlight' we had years of consistent and cumulative events depicted that slowly took him to the point he had to make it.
'If the Apocalypse starts, beep me!' - Buffy Summers
'The sky's the limit.....' Jean-Luc Picard, 'All Good Things'
courtesy of Saquist