That does assume that reddit actually updates the comment entry in their backend instead of keeping histories of the edits which I'm not sure we've had any insight into.
That’s my assumption too, keeping a history for every user increases complexity tenfold, while flagging deleted comments seems to be a common practice even in smaller companies because it’s so simple.
Another user said they tried the data dump GDPR request and the comments included deleted comments but only the edited version, so I guess this can be verified at least.