Yes, Diurnal has more overheal because of HoTs. Adjusted for overheal, I'd say Diurnal is still about 20% stronger. This is when under near maximum stress in terms of healing output, and assumes you are paired with a WHM and not a SCH, where your shields can overwrite and skew the numbers. Also, a WHM at maximum HPS heals for about 35% more than a Diurnal AST, and about 75% more than Nocturnal, for anyone who cares. A SCH can also easily match (or beat) your maximum HPS in Nocturnal while still outputting 200+ more DPS than you depending on the fight.