Chronological nitpick: SingInst (which later split into MIRI and CFAR) is significantly older than the EA name and the EA movement, and its birth and growth are attributable in significant part to SingInst and CFAR projects.
My experience (as someone connected to both the rationalist and Oxford/Giving What We Can clusters as EA came into being) is that its birth came out of Giving What We Can, and the communities you mentioned contributed to growth (by aligning with EA) but not so much to birth.
Chronological nitpick: SingInst (which later split into MIRI and CFAR) is significantly older than the EA name and the EA movement, and its birth and growth are attributable in significant part to SingInst and CFAR projects.
My experience (as someone connected to both the rationalist and Oxford/Giving What We Can clusters as EA came into being) is that its birth came out of Giving What We Can, and the communities you mentioned contributed to growth (by aligning with EA) but not so much to birth.