Regardless of whatever happens in that 1000+ years, Goku has still cut down that opportunity. Yes you being erased and the world being erased aren't the same thing, but to one's perspective, simply you being erased vs everything being erased is the same experience. You still end up in nothingness either way, and for you it wouldn't "matter" if you are erased or if everything is erased, because you're nothing anyway. You won't percieve anything at that point.
It mattered because it was relevant to your belief of "nothing matters if everything is erased". Naturally I bring in real life because that's the basis we often use to impose standards (to some extent) when judging fiction.
And you're saying nothing matters if everything is erased in the sense that nothing you did before will "live" if everything is erased. I'm saying the current waking moments of life matter and it's worth enjoying regardless of what happens at the end. That's why that 1000+ years of life matters regardless of if it was going to be erased at the end, and why people have a right to be mad at Goku since their experience is getting cut short because of him.
In Dragon Ball, you don't disappear when you die unless your soul is destroyed. So to them, there is a different between living a long life and dying vs. living a long life, dying, and then getting erased in a century. In there case, whether they live a long life or a short one, or rather they exist for another 1000 years really doesn't matter since their very existence is blinked out. At least with Goku they have a remote chance of not suffering that fate vs. it's going to happen it's just a matter of when.
Let me put it in another way. If you had the chance to save yourself from an illness, but you have a high risk of dying from it vs. letting the illness take its course and live for another year, which one is more worthwhile to you? This is a personal question that has no right or wrong answer, but most would usually chose the course where they can prolong their life even if failure meant death instead of just sitting back and waiting for the end. This is especially true in Dragon Ball where almost everyone has a warrior's mentality in that they don't believe quietly waiting for the end even if they're promised several more years and will chose to fight even if the odds of succeeded are nonexistence or that they would have lived longer if they didn't resist.
And as you said, you're injecting a personal belief system in a show that has a clear cut way the afterlife works. So personal belief shouldn't be a factor. The people in Dragon Ball, quite frankly, are not thinking 'we're could have existed for 1000 more years or it wasn't for Son Goku'. Everyone agreed that Zen'o was going to wiped them eventually and their ire towards Goku is more petty since he's friend with Zen'o. Only the trio from U9 had any real justified anger and that was mostly Goku's 'I don't give a damn' attitude about everything. Fans being mad at Goku also ignores that the people more at fault here are the gods since the reason why the mortal levels are low because the gods haven't been doing their jobs. So the narrative that 'Goku 'rob' people out of 1000 years' seems really crazy when the narrative should be 'why the hell aren't the gods doing their freaking jobs', especially with Beerus who did nothing when he fellow gods were being slaughtered by Buu and even trapped one of his equals in a sword.
