Its just that I see people use a lack of population in 'niche' communities as a failure of Lemmy overall, and using some subjective made-up number to justify Lemmy's overall failure, when there's obviously traffic to major communities and 'life'/activity on Lemmy on a daily basis.

It's not so much a "failure" of Lemmy as it is an assessment of the situation (at this point in time). I wasn't suggesting Lemmy was or will be a failure, nor that it's dead. I like it here and I'm active most days. There still isn't enough activity in niche subs for Lemmy to have mainstream appeal, though. Even a broad subject like Poetry is carried by a handful of people, and that is a fairly lively "niche sub".

We're currently still in the phase where determined, committed individuals have to spend concerted effort into keeping small subs going, rather than them being self-sustaining.

I do like it here, though, and I really hope the growth continues.