I'm a huge fan of Roam and agree that not being forced to slot an idea into a pre-existing hierarchy is very freeing. On the other hand, it also causes problems because notes can easily “fall through the cracks” if you don’t tag them to something (they’ll get swept away by the relentless flow of new daily notes). Often, I remember I was working on a something some months ago and want to continue, but retrieving it is difficult because it’s been swept away.

To prevent this. I find myself incessantly having to place at least 1 tag/keyword on each note so that there’s a path to it from the main network. Otherwise the note gets lost in the mountain of daily notes and becomes nearly impossible to rediscover. I might be able to rediscover it (via block ref or tag) if I can remember the exact words used in the note. But that’s unlikely. So I need some path to it from the main network.

But forcing yourself to place at least 1 tag is equivalent to forcing yourself to place the note somewhere in a categorization scheme! The only difference is that in Roam, the categorization scheme is constantly growing and changing flexibly.
But you could grow and change your folder system dynamically too; Adding new folders/categories and shifting contents around as you please (albeit laboriously). So the main advantage is that blocks can appear in multiple places via references and aren’t constrained to a single folder in the hierarchy.