There are other sites with similar features and layout to Reddit (Voat, Ruqqus, Saidit, Raddle, communities.win, etc.) but none are really in competition to be "the front page of the Internet". This is because Reddit has a huge community with varied interests which provides self-perpetuating advantages. For example: the activity level is generally higher; if you start a subreddit for a niche topic you have a chance at finding an audience; great comments/submissions will garner thousands of upvotes rather than a few dozen (smaller sites have a proportionately tinier vote ceiling, making it hard to differentiate between "good" and "amazing").

I can see increased retention/monetization maybe leading to a larger user-base in the short term, but if it makes good content less likely to crop up, or leads to less discerning users (ingenious effortposts lose out to low-effort pandering memes), or even if it just narrows the interests/hobbies represented on there, then over time it will destroy Reddit's main source of value.