Both gambling and doomscrolling can be harmful when done excessively and without balance. The comparison between the two, however, is not so simple: gambling, in some cases, can be seen as a form of entertainment. Doomscrolling, on the other hand, rarely offers this positive side, as feeds are often full of negative news and content.
Both can be a time waste if being done excessively. So, doom scrolling it typically you just end up with long hours doing social media. And I think it's a common thing to do today because of the smartphones. It's very easy to do and with gambling, the same thing but you won't do doom scrolling there and it will require you some pennies to do it. If you're into the free time wasting, doom scrolling is the choice and yes, both can be harmful and could cause emotional damage heavily.