Very convenient.

What do you expect me to do? Hack reddit's Postgres databases to recover deleted comments?

There are several tools for viewing them, primarily based on Pushshift, an apparently individual-run database that grabs whatever it can from the Reddit API, usually within a few minutes. The frontends come and go; currently the major ones are unddit.com and reveddit.com (which honours user deletions, refusing to show them).

There are also Pushshift-based sitewide search engines: redditsearch.io is made by the Pushshift creator but doesn't show deleted content. ihsoyct.github.io does, but is unreliable, often randomly missing some comments and posts in any one run of a query.

With the amount of constructive comments/posts removed for seemingly no reason nowadays, and the blight of users overwriting and/or deleting helpful, otherwise anonymous comments when making privacy purges, I find it now more pleasant to browse with all deleted content shown than without.

Offer up something more than a vague "I saw this thing one time, trust me on this"?

I saw this thing many times. Trust me on this.