The only problem with the bloodline thing is, Sheb and Sheemie are also still alive from before the fall of Gilead, and I'd be quite surprised if both of them happened to be indirect descendants of Arthur Eld. It seems more likely that time just kinda skips past people occasionally, without affecting them in any way.
Yeah, this always confused me a bit. My best guess is that he was actually todash for around 10 years, but it was such a confusing jumble of messages that forgot almost everything he saw, making it seem like less time went by.