I could be wrong, but I recall in Excalibur 50 that Otherworld was rebuilt by Merlyn following the Feron-Phoenix-Tower spell that created the Energy Matrix... Otherworld was where they traveled and found the original tower. Didn’t Merlyn day that Earth was long-dead? That its population had all perished or otherwise expired? That’s my first question, I guess. Whether Otherworld started as an empty ruins Earth.
Nope checked 50. The OG tower was on 616, built by “ancient aliens” or something. Otherworld was “established” by Merlyn, but not adequately described.