A slot WR will run different routes like slants and drags that are designed to lose DBs in the wash of LBs, RBs, and TEs that may be within 5 yds of the LoS. Yes the nickel guy could line up anywhere, but a DT who specializes in stuffing the run can line up at DE and rush the passer too, they're both DL afterall. The difference here is nitch ability and effectiveness. Powers is really good in the nickel position and he also plays outside well. Time will tell where Canady is best suited, good luck to him.