Agree on many things here, but SQLite does support WAL mode which supports 1 writer/N writer readers with snapshot isolation on reads. Writes are serialized but still quite fast.

SQLite (actually SQL-ite, like a mineral) maybe be light, but so are many workloads these days. Even 1000 queries per second is quite doable with SQLite and modest hardware, and I've worked at billion dollar businesses handling fewer queries than that.