In talking to Leliana, Dorian says, "Alexius sent us into the future. This, his victory, his Elder One -- it was never meant to be."
It's rather odd that one of the paraphrases for the Inquisitor is "This isn't real," because that's not what is reflected in the actual words.
[1. I’m sorry for what happened.] I’m sorry for everything you suffered.
[2. This isn’t real.] If we get back to the present and stop Alexius, then you’ll never have to go through this.
[3. I have to get back.] I need to find Alexius and reverse the spell.
Nothing in any of those lines indicates that they don't care, or think that none of this was real. In fact, if you ask Dorian at the start, "And what happens if we can’t get back?" his response is, "Then we get comfortable in our new present."
When Leliana lashes out at Dorian -- "This is all pretend to you, some future you hope will never exist," -- she is wrong. Her reaction is understandable in the circumstance, but it is not a fair one.
Interestingly, I read the same lines and I come to the opposite conclusion, except in the case of the Inquisitor's choice 1.
-"You'll never have to go through this". Sorry, but what? I've already gone through this! That 'you' is Past Timeline Leliana. I'm not that Leliana." In fact, that's her answer: "I suffered. The whole world suffered. It was real".
-"I need to find Alexius and reverse the spell". "So everything can be solved with undoing a spell? Great! What about all the suffering we went through? Can that be undone so easily?". The answer is "no", of course.
And then, of course, it's Dorian's words. "It was never meant to be". It happened, and who says destiny should be otherwise? Aren't we angry at Solas for not accepting this reality that has brought pain and devastation to his people? He could say "it was never meant to be" too, and indeed, we know now that the natural state of reality should be a world without the Veil.
So, yeah, with the same information, I come to the same conclusion as her. And she is being fairer than you give her credit for, because despite it all, she's still willing to fight and sacrifice herself so the Inquisitor and Dorian have a chance.
I suppose this is just you and I looking at it differently.
To me, all of those people are still alive in the Inquisitor/Dorian "present" timeline, so the lives are not being "erased." And in fact all those that were were killed since then will be restored. If you look at the timeline from the perspective of Inquisitor/Dorian, hundreds of thousands (or more?) people died in the space of a few seconds (or however long your loading screen is), and they are actually bringing people back to life (again, from their own perspective).
Their perspective is not the only perspective, and that's the point of Leliana being angry at them.
At any rate, I don't feel that it is a good comparison with what Solas wants to do.
The comparison is faulty, but for different reasons.
-First, the Inquisitor is innocent about Alexius playing with time, while Solas brought it on himself.
-The Inquisitor has friends they want to save and reasonable expectations about the future they want to build, even if it means damning a timeline, while Solas would damn the world to bring back the remnants of a civilization (not its people) and the only people who will be saved is a group of tyrants who are his worst enemies. Given his track record, I don't trust his contingency plans.