Tyler Lockett is one of the most dangerous weapons in football, but ability alone does not a fantasy star make.
His per-catch Reception NEP (1.35) was slightly better than teammate Doug Baldwin's 1.33, and his per-target rate (1.00) was nearly as good as Baldwin's (1.01), as well. And Lockett maintained those marks on 69 targets, so that's a solid sample. We should feel excited about his potential.
The real issue with Lockett, however, is usage. Even with Seattle's drop back numbers trending up each year since 2012, their 535 pass plays ranked 27th in the NFL in 2015, and their pass-to-run ratio was 29th.
Combine that with the fact that Lockett is probably at least third on the depth chart behind Baldwin and Jermaine Kearse (and possibly fourth behind Paul Richardson, too), and taking Lockett in the sixth or seventh round is asking for disappointment.