Let’s look at some numbers and do some napkin math:
Currently, the top post of Lemmy can usually get a little more than 2K upvotes, which puts Lemmy at about late 2010 to early 2011 reddit level of activity, which is right before reddit hits its explosive growth phase in 2012 with SOPA, Kony, and the Obama AMA. While active user count has been going down, the amount of post and comments have both been steadily going up.
You also have to realize that in more than a decade, there was never a reddit alternative that has EVER hit this level of activity. (unless you count 9gag or the_donald for some reason.)