They claimed that "The people who do the real contributing—posting, modding, defining the culture and building the communities that Reddit benefits" were driven off ("these people have been purged already over the past 2-3 years.")
Small groups and individuals can be extremely important. It's less about the raw numbers of 'how many <X> did we gain/lose' and more about 'what kind of tone are we setting'.
When Reddit allowed /r/the_donald to flourish, what sort of message did that send? When there was a purge in/of leftist communities, what sort of message did that send? Politically, what Reddit allows is actually quite narrow, and it's trending toward mainstream sanitized neoliberal center-right (aka 'advertiser-friendly').
When Reddit started to corral everyone into one shitty app by breaking the mobile web experience, what message did that send? And now, what message is being sent with this API cash-grab?
Reddit's positioning is constantly chafing against Reddit's core demographic. The people who operate Reddit don't understand what they want (aside from $$$), don't understand their customers/content providers, and now seem unwilling to even listen to their customers/content providers.
Many messages stacked up over the years eventually form a story. What's the story of Reddit?
Only some small groups were actually driven off.