I agree: too tight! But here's a blogger who says 1 hour is enough in Seattle
https://www.sanspotter.com/is-1-hour-layover-enough-time-in-seattle/#:~:text=The good news is that,re making an international connection. However, he doesn't address the international to international connection, which is likely more complicated than just staying airside and avoiding security. This page from the airport goes into great detail:
https://www.portseattle.org/services-amenities/international-arrivals-and-passport-control