Why would we protect less players than we're able too? We don't know what will happen with our forwards but two seasons from now I doubt that our defense will change much outside of Bouwmeester and Gunnarsson being gone with internal replacements. I'd be surprised if it did look much different.
It's not out of the question. Edmundson is a quality player but he isn't completely irreplaceable. So I don't see why we would protect him over our better defenseman especially if Walman is ready to go.
It's entirely possible we have an overload of young forwards and can package some of our lower end talented forward prospects (Blais, Barbashev, etc) in a deal to keep Edmundson.
You are viewing it from the wrong perspective. It doesn't matter that we'd be protecting less players than we're able to.
There is only one question that matters... is your fourth defenseman more valuable to your roster than your fifth forward? If the answer to that question is yes, then you protect 8 skaters. Seattle can still only select one player.
The forwards that would require protection are: Tarasenko, Steen, Schwartz, Schenn, Berglund, Jaškin, Fabbri, Thompson, Stevens, Barbashev, Soshnikov, Sundqvist, Sanford & Blais. Plus any established NHL players we add between now and the expansion draft.
We don't know if there will be 5 guys who are unquestionably more valuable in 2020. We can safely say that 3 will. If Thomas and Kyrou/Kostin/Foley develop as we hope, then the 5th guy could be a third liner on our roster. It's far easier to replace a good winger than it is to replace a quality defenseman that works well on your team. Schenn is a UFA in 2020, our roster composition might mean we can wait to sign him until after the expansion draft. Most other teams are protecting 7 forwards, it makes it easier to trade a high value forward before the draft and get a good return. Etc.
There are way too many variables between now and then to know what's going to happen. Protecting 8 skaters could make the most sense, like it did for Nashville last year.