Whaat! I haven't finished one yet and it's taken ages (I'm a bit slow you see) so I have to do it more than once for any benefit. They must be mad (or I am).
Yes, the two current Settlements are mind numbingly boring, and the Vikings especially are a true slog fest to endure...
Japan at least has the Merchant mechanic which removes most of the actual challenge, and requires 2 fewer completions vs. Vikings to fully evolve the main prize.
That said, it's well worth the massive effort & time sink, since both the Yggy Tree + Shinto Temple are beyond stupidly OP.
No event building yet comes close to matching these things, and only high leveled GB's (ie: think at least Lv20-30+) will out preform these babies.