> In fact I don't recall ever seeing an ad for tiktok and yet it is humongous

Then maybe you're not the target audience, or you're just not noticing the ads, because TikTok is particularly notable for their aggressive marketing efforts during their growth phase.

> Non big tech solutions need solid UI and UX that does not assume your average user can balance a binary tree

Non big tech platforms don't need anything. They can never compete with billion dollar budgets and they shouldn't set that as a goal. Everyone enjoys a well designed UX, but billion dollar marketing budgets will always eclipse the alternatives.