Reddit doesnt produce any content itself, so viewing and commenting in general isn’t particularly important. What matters more are valuable contributions.
What even constitutes value in this case, though? And if viewing isn't important, then why have "valuable contributions" at all? The purpose of reddit is to sell advertising space. They leverage the website's audience for this purpose. Reddit's users are the product being sold. The content is how they draw in users.
There is already an army of repost bots which aren’t going away. The bots don’t care about the health of the platform, so we can assume they are at maximum repost saturation.
We really can't assume that, though. Also, "maximum repost saturation" would, by definition, be literally all content submitted via repost bots. They're not there yet. Not by a long shot. But the share of posts submitted via automated means is definitely climbing.
And reposts still require new content generation to make reposts. You can’t repost the same stale content perpetually.
A huge portion of reddit's content links externally. It's literally a link aggregator. It's not difficult to have a system that aggregates links and website headings, dumps that into a database, and then a bot parses out new entries and builds submissions from those based on some arbitrary set of metrics. The content is still generated, but it's generated externally and then consumed by the system.
But it’s popularity and userbase can dwindle over time. Tumblr still exists, but it’s a shell of its former self.
The Tumblr situation is complicated. Yahoo, the company that owned Tumblr at the time, outright banned all pornography on Tumblr because the site had a pretty bad CP problem, which they couldn't think of a better way to handle. This was at a time where porn was integral to Tumblr's ecosystem, far more so than it is, or arguably has been, for reddit's. Reddit has also done the much more intelligent and careful thing of slowly squeezing out adult content from the website in order to appeal to advertisers. It's been happening for literally years, coinciding with a not incidental decrease in average user age. Reddit ownership seems a lot more aware of the website's value proposition and is careful not to make overwhelmingly drastic changes to how it operates. Yes, quality is decreasing, but it's like boiling a frog. Quality has always been decreasing, and if that's the case, it's hard to notice because it's always been happening.