I couldn’t download the timetable on my phone but, while not prolific, there will be a number of options over PDX for AS. Certainly DEN on UA or WN will/would offer more.
Correct about AS and PDX but remember, AS will also fly to 2 more hubs -- SFO and LAX -- as well as their 2 focus cities -- SJC and SAN -- from PAE. So, depending on what skeds AS is able to offer, there should be some network connections available over 5 cities that AAG will serve from Everett.
However, I'm not sure how many connecting pax AS plans on carrying from the new airport north of SEA. With EMJs being used, O&D traffic may very well account for the majority of their pax. All 8 of their routes from PAE are to cities that have lots of flights to SEA and I assume they figure PAE will simply tap into that local traffic to/from SEA/TAC.