Forum won't became a worse place by deleting 3 years old posts, but I don't think it will become noticeably better either. At least not enough that its worth it to report those old posts. After all, I don't think that only important metric is number of deleted posts, but also where and when those posts are written as well, but unfortunately that's info that we don't have access to.
In my opinion, 1 report of a post written today by a signature campaign shitposter is worth more than 100 reports of old bumps and similar shitposts written 3 years ago by some low rank shitposter or paid thread bumper. And that's why I like this new change, because those who like to report can actually focus their energy on something that affects this forum much more.
But no one will suffer if these posts disappear. It is worth discussing the meaning or meaninglessness of something only if it concerns everyone. If some activity is strictly voluntary, then why these arguments about whether it makes sense or not? Personally, you or the forum will get worse from the fact that someone has committed low-value actions (in your opinion), and sent 1000 reports to old posts? I believe that 100 deleted reports from 2020 are a million times more useful for this forum than 100 empty discussions about what is valuable and what is not, what makes sense and what does not. Empty talk.
Now we see that no one else directs any energy anywhere. Nobody cares about these reports.