Play what makes you happy, I have played Holy for 10 years when we were good and when we were bad ,yes I could have changed to Discipline and topped the charts but it was not what I enjoyed playing and I completed every raid at the highest level still. Sometimes I miss the days when we had no logs and raid comp was whatever classes we had instead of what we think we should bring and a person could simply play what spec they thought was the most fun.

There is a lot of talk of how they have ruined Discipline but I do not find this to be true Discipline has a viable role in raid, is it the god of healing it was in WOD no, however, Holy while improved a lot from WOD is also is not going to be the god of healing in legion. Both specs bring different toolkit's that are going to benefit your raid regardless both can off DPS when there is no healing needed.

Discipline has some amazing attributes it can seem clunky at first to play it can really shine in high damage fights if you have a Dpriest who knows how to play the class they are going to be amazing. I look at holy as more of a toolkit healers now we have seen our healing increased, but we still are largely support healers as well.Our two main raid cooldowns Hope and Hymn are support spells one we buff the rest of the healers while we healless players than before but still at an increased in output and the other we give free mana ( yes I know there are a lot of different and amazing spells that Holy has outside of these and I love Holy I am simply pointing out two spells). I think regardless of what spec you play you are going to be fine but I do not see them buffing Discipline to be better compared to any of the other healers in this expansion.None of us should take anything we read on one site as gospel and need to make sure to look at multiple guides, sites, and logs before sinking artifact power into one spec as I am sure you will.