Depending on your perspective. For "next Google", 35k subscribers is nothing. For a search engine, which has been assumed to be free for the whole decade, 35k paying users is a miracle.
My perspective is "tech startup" that reaches the front page of HackerNews on a weekly basis.
There are plenty of billion dollar companies that make users pay for something that has always been free (note taking apps just off the top of my head).
Subscriber count is not a measure of quality or importance of the service category. Hacker news is less popular than TMZ or the DailyMail, but it is not a lower quality news website.
Despite having so little paying users. Not even 35,000 lifetime paying users.
They can really thank the HN echo-chamber, because without it they would have been forgotten a long time ago, nobody knows about Kagi outside of here.