Don't mind the dollars, don't much care for the 4th year, but here are the reasons he was signed:
https://www.youtube.com/watch?v=hxC3o2vw1b0
Oilers Record 2016-17 without Russell = 6W 8L
The Oilers clearly value his battle (Eberle possessed none of and that was the main reason he was traded), he knows the system, and coach trusts him. We are in a tricky spot right now with our future 2nd pair apprenticing on the 3rd pair. Maybe they need one more year, but probably 2, and then they will be good to go. Bringing in a completely new 2nd pair to start the year would cost a ton and you don't know if the guys are going to fit in the room. You have to be very careful with the team chemistry right now. It's good for the first time in a decade and we got rid of one of the few guys (Eberle) who wasn't totally buying into the program. I'd play Russell at 2LD until Sekera comes back and would bring in a single vet RD (like Franson) on a short term deal to cover short-term. Keep Nurse and Benning on a short leash for one more year and then you get them on a bridge contract and then make the Russell and Sekera deals go away when then need to be signed longterm.
Chia said yesterday that they have 10 dmen in the system born between between 94 and 98. So spending assets to bring in an expensive #4 who may or may not "fit" could be problematic. Russell cost nothing but cash and I'm pretty comfortable with him covering the bet for the first two years. I actually like him a lot as a #5 who can play 2nd pair on either side when injuries hit. You can dump that contract in year 3 or 4 pretty easily.
So while I don't care for year #4, seems like that was the cost of doing business, and Chia has telegraphed that the strategy is keeping guys who buy into the system, battle hard, and develop the young dmen we drafted ourselves. The cost of acquiring top 4 dmen in trade is just too damn high and nobody wants to give one up unless you are dealing with the Bruins it seems.