Regardless of whether a person's lived experience is time-boxed or eternal, either we think the good experiences outweigh the bad or we don't. If the good experiences outweigh the bad they still outweigh the bad even if they're eternal.
For me, I believe good experiences do outweigh bad. And summed across the entire population of all humans who have ever lived, I believe they do too, although of course there are some for whom they don't.
Buddhism is basically (basically) predicated on the idea, I don't see why it's horrible to acknowledge the possibility, especially if it could be true.
I wonder if a lot of the original Buddhist cosmology was based on the experiences of meditators having what we now call psychotic episodes, which they would have seen as a glimpse of reality.
Buddhism also says that an end to suffering in this lifetime is incredibly rare, something that qualifies you not just as an arahant but as a full Buddha. The claim that full Buddhahood is possible is obviously interesting - it implies that meaningful developments in enlightenment are very possible even after the conventional four stages of awakening - but obviously it's something that can only be explored by arahants who have completed these four stages. (And there's enough controversy about even the mere existence of modern arahatship, so the claim that it might at some time become common enough to make further progress feasible is even more speculative!)