What's top DPS can change, and usually does change. I feel like going "all in" on the theoretical best spec when it's still largely based on projections and numbers that will be tweaked isn't really the best plan unless you also happen to like that spec.
I'm going to prioritise the spec I enjoy and then I will focus on catching up an offspec artifact or two for the fights in which my main spec is not ideal. I try to balance what I like with what is best for the raid. That said, I'm primarily a heroic raider, so it's also not a big deal if I'm not 100% min/maxing the top spec.