Well guy asked for most defensive devotion setup so although I think turtle and/or dryad are not worth taking no one can say that they arent defensive devotions and that they do not add some measure of defense.
Stating that for specific builds it is possible to make devotions even more defensive oriented than the setup I proposed, I tried to be universal as much as I could, and also, personally, I would never go that devotion route.
A lot of people hate Turtle but I think it’s decent enough as long as you layer it with other defenses. If you’re unsure about it you can always take the points into and put them into filling out Scales of Ucama for some +% health and a good life leech proc.
Speaking of which, if you have a skill that can hit lots of targets on a low cooldown, really consider using Wendigo’s Mark. It has no cooldown so you can rapidly drain life from tons of enemies with it.
Anyway what JoV posted is very similar to what I used to use on 80% of my builds. I wouldn’t use it exactly as is, but in the context of what you asked for, it’s very good.
Although I cant agree on turtle, scales and wendigo are really good defensive choices also, tho I do tend not to take them if my vitality dmg is not supported.
Stating that I dont mean supported as a main dmg type but enough to have at least few hundreds +% to vitality (occultist provides that easily from possession, BoD and soleals line, w/o any gear addition).
Crab is more than good and definitely better than turtle but problem with it is a bit unlucky requirements if you dont go ascendant (purple) route. Best tankines overall is provided by primordial/order combination of devotions, I would be free to say even way to much when compared to other options.