I mean, is Threads really soaring, though? I think I just recently read somewhere that usage is down by half or something...even 100 million users will disappear quickly if they keep diminishing by half.

In left-leaning media it's soaring, they decided. In right-leaning media it's completely dead. Vice versa about Twitter.

In reality Threads is fine. 100M was never going to be a stable userbase, it's just initial hype and sign-ups. But they have now a chance to grow it, and few dozen million active users is a sufficient start.

50% retention month on month for a free, low-friction service would actually be very, very good. Tbh, I'd assume it's lower than that; 50% is unrealistically high.