Realistically they are as similar as they are different. The general consensus is that strategists think and define, planners adapt and enact. I am a strategist. I am a planner.
See, they are not too different from each other and in both cases I wrote in the first person, why?
Because I am both a strategist and a planner, a strategic planner if you will, although I never use this term as it is confusing to both the client and the agency as it does not really define what you do but says you do everything.
Because the evolution and nuancing of agency life and thinking around brands and how consumers interact with them has, for want of a better term, become polluted over the years. When in a permanent role you will be either a planner or a strategist, as a freelancer and consultant you can change your modus operandi to for the project needs a lot more.