According to PFF (and snap counts are one of the few things I trust them for), Edelman ran 49.5% of his routes from the slot last year. 76.6% when Amendola was sidelined, and therefore most of his snaps must have been outside the slot when Amendola was available. Side note: this isn't exactly what I was counting for Edelman in my previous post (PFF is counting passing routes, I counted snaps regardless of whether they were a run or pass).
So I think there's a couple of important things to keep in mind, here. 1) Most receivers run a non-trivial percentage of their snaps from the slot, even guys who you would never consider slot receivers. The same PFF article states that Dobson ran 15.9% of his routes out of the slot, and he's by far the most definitive outside-the-numbers-definitely-not-a-slot-receiver we have.
2) When Edelman was in the slot last year, it was largely out of of necessity. Amendola was clearly the slot guy when available (same as this year), but then he got hurt. Since the imprisonment of Hernandez (who himself took a ton of snaps from the slot) effectively killed the 2TE offense, the Patriots ended up running a ton of 3WR, with their top choice of slot receiver being gone for a signficant chunk of the season. Add in the fact that Boyce (who took most of his few snaps from the slot) and Gronk also went down, and the Pats were left in a situation where they had to run a lot of 3WR, it was vital that the slot receiver be a guy that Brady trusted, and Edelman was the only player left healthy on the roster who could handle the job. When Edelman was running routes out of the slot (which, again, was less than half of the time), it was pretty much a function of necessity since all the other guys that could do it were injured or in prison.
And on top of all of that, the eye test just tells the story, IMO. He's a lot more "outside WR who is capable of playing in the slot as needed" than the reverse. And generally speaking, any sub-6-foot receiver who lacks burner speed can be characterized as such, so that's not much of a statement on anything, really, except the fact that he's kinda short.