I think this is unironically a big problem with Lemmy. The sorting is way, way, way too fixed and inflexible. You can sort by active which ends up being the same few communities. Hot is too much like it's kinda new. Top Day is usually what I use since I want to see the most popular posts first each day, but then more niche content is just hidden.

There is no best sorting order, because the best sorting order would be a combination of multiple sorting orders. This is one thing reddit really excels at with their sorting orders, they seem to have like a "combined" approach, like an intelligently-designed system of sorting algorithms to show people good, active content while not hiding important things.

On a community/platform like Lemmy where it's less popular and less active, having proper sorting is even more important.

Like you said though, this is entirely fixable, and something Lemmy definitely can improve. The question is, will they improve it? I certainly hope so.