They are losing 1. Quality in UGC; 2. Quantity in UGC; and 3. Unpaid mods, which are all considered most important assets in terms of their (Spez’s) IPO.
Are they losing enough to have an impact to their ad traffic however?
Something reddit definitely have lost is the monopoly on online communities, now there's a bunch of alternatives that people use which has definitely reduced the value of reddit.