Yeah, those numbers are consistent with what I would expect to see. It gets better... mainly the better you get at increasing your Click-Through Rate and your Average View Duration the more impressions you'll get from YouTube. Which of course leads to more views and then more subscribers. At the same time your current videos will continue to perform for you, so amassing that library is really important.
But all in all I would say you are on track with exactly what I would expect to see with a channel that is learning/implementing good SEO practices.