It still influences the user base and gets unaligned instances defederated from many of the larger instances. The main advantage of Reddit (number of users) is lost and the disadvantage of your reputation following you around different communities is retained.
It's good that Standard Oil existed and probably good that it was ultimately broken up. In the modern connected world that might not be necessary due to international competition.
Having said that, Google's recent behaviour re: search and esp email proves monopoly abuse can still take place if your initial service is good enough to capture a huge slice of the market.