The problem with stat mixing like that (Save for the STR ring), is well, you have them so split apart that each one does an incredibly insignificant benefit for you.
5 Piety is a waste for a Drk, just learn to manage MP better. 1 Piety gives you around 5.3 total MP. 5 Piety for an extra 25~ MP is in no way a benefit at all. And as far as the MP regen goes, 30 Piety at level 50 gets you +4.8 MP per 3 seconds in combat. Now try to imagine what 5 Piety gets you. You likely wouldn't notice any difference at all in your MP regen, especially when 99% of your regen comes from your own abilities, which as far as I'm aware is not effected by Piety. And then there's Darkside, which practically makes your passive MP regen useless, as it instantly eats it. Sure Darkside may eat like 3 or 4 less MP, but in the grand scheme of things, when your MP is constantly jumping around in the thousands, that is nothing.
Vit is ok if you're full Vit, but 10 Vit is literally only giving you 20.5 HP per point. That's a whole 250 HP you have there, which isn't going to make that big a difference in your pool of 15k+ HP, and is something easily covered by food, plus more, if you need the HP that bad. The reason people often go full STR attributed is because of this; Vit only effects your max HP, and you only need a certain amount of HP before anything above that is wasted. And no, it does not give your healers extra time to DPS, because any blow that would otherwise reduce your HP enough to where your healer needs to give your attention, is still going to take your HP that low. It's an instant spike of damage that takes a chunk from your HP, putting you into zone that signals that you need healing, or you will die. They will still be throwing heals on you after that hit, because at any moment if even an auto attack crits you at the wrong time, you could easily drop. If they're not healing you, then they must enjoy watching their tanks panic blow all of their CD's to attempt to stay alive.
Splitting stats like that creates the same problem Drk has as a tank overall. It's so even it doesn't excel at anything compared to the other two tanks. Your stats are split so much to the point where your stats in all areas are giving such a minor, nearly unnoticeable effect.
But I mean if you're enjoying it and think it's working out for you, then you rock that 5 Piety. But the only way to play Drk on the defensive side is close to the way you would play a Pld, except there is more to it with less return. You literally just hit your CD's when a big attack is incoming, that is all there is to it's defensive side. And even though it's closer to Pld in terms of tanking, it takes some pointers from Warriors as well in terms of it's offensive side, though not quite as good. STR attributes and slaying accessories is a universal thing. The ultimate offense is the best defense. The faster things die, the easier the fight is. It doesn't necessarily mean that someone is trying to play Drk as if it were a War or a Pld, but even if they were, they'd still be capable with the job, up to it's own limitations at least.