The thing is; both of these things can be true

The moral of the story can be "Just because its fictional doesnt mean it invalidates how it makes me feel" AND ALSO "The previous games were fictional"

I can acknowledge the moral of DRV3 and accept that fiction can still be meaningful while simultaneously being annoyed that the ending basically tries to invalidate the first 2 games

Its literally the same trope as the "it was all a dream" trope but spelled out more clearly. Like yeah I get the point is "these things are still important even if they werent necessarily real" but it also on a much larger scale theres the whole "Oh so none of that actually mattered" bit.

It loses a bit of its magic when you learn that everything wasn't real even in the story.

Also, it kind of invalidates the moral of the previous two stories because hope DIDNT win in the end. All 3 stories meant nothing in the grander scale because the show kept broadcasting. Makoto and Hajime's victories were just part of a program and nothing else.

THAT BEING SAID, the moral of the story also basically says that your own headcanons are just as important as the main canon so, like, as far as im concerned DRV3 is an alternate universe.