Yes and No for this. While I agree TD upside is volatile, there are some players who are just exceptions to this for whatever reason. Dez, Odell Beckham, Adrian Peterson, and Rob Gronkowski are just a few names of players who have such a solid and predictable TD floor. A-Rob may potentially be in that group although there isn't enough data to confirm this.
Dez getting volume is a myth btw. During the 2014 seasons (which is the closest statistical season we have to what we expect this coming season), Dez had, iirc, 145 targets (maybe less). In comparison, Brandon Marshall had 173 this year, Demaryius Thomas 176, Julio and Antionio Brown eclipsed and got close to 200 respectively, ODB had 159. Due to the nature of his offensive, Dez gets relatively low volume, but gets by on being remarkably efficient and, of course, consistently scoring way above league average in touchdowns (16 that season).