A few observations:
Be wary. Money isn’t everything. I believe one of Roam’s senior engineers has recently left or is leaving, and I’m a member of a Discord community with a bunch of ex-Roam plugin developers who now are building on Obsidian. This may be a fad thing, as you say, but I think there are deeper issues afoot.
This is another important factor in Roam’s usability. Roam is quick with fewer notes, but it gets very slow with a lot of notes. This is another reason some prominent users of Roam have left it recently.
I realize it looks like I’m shilling for Obsidian here. I’m not—sincerely, use whatever you want!—but I wanted to add what I’ve heard from the Roam expats I know.
Oh, man, is this a metaphor fight? 
For me, keeping tasks together with the work is like someone undid a corpus callosotomy. Suddenly my plans are aware of the work I’m planning and vice versa.