"I never read those books"
And? Just because you're not qualified to comment has no relevance on the argument.
"Oh, we're counting alternate timelines that get erased from history?"
Yes, we do - especially when whole trilogies narate/focus on these alternate futures as opposed to a few lines, comprising a few seconds in an episode.
"You mean like the destruction of the original starship Enterprise
? (Star Trek III: The Search for Spock
Yes, like that. Except that was a single occurrence in a line of optimistic episodes/movies (adventures on the background of a federation at peace and expanding); DS9 and the voyager fleet are occurrences in an ongoing crap-sack trend.
"Future's End" "Timeless" "Relativity"
Really? You call these dark futures? In 'future's end' you had a few seconds of doom prediction followed by 2 pretty light episodes.
The other 2 examples - not even these few seconds.
As for the other episodes you mentioned - do name the ratio of these to optimistic episodes throughout Voy.
I already told you, Sci:
Gross hyperbolics wont make your position less hollow.
Indeed, the very fact that you must recourse to such cheap tricks to support your position highlights its fundamental weakness.
These days, 24th century trek lit is comprised of consecutive wars/destructions (narrated in detail). You get perhaps a reconstruction blues book or two, then on to the next disaster.
As for the rare optimistic book,you know how you can tell it's the exception? Because its premise is, by necessity, grafted onto the crap-sack events that have become the core of 24th century trek lit.