Deathchill is extremely questionable for tanks, yes. It even is for DPS. It's not that it ain't good, it's just too weak for a point in a tree with plenty other options. It has uses mostly in PvP, and in the very rare situation where it absolutely positively matters you start with humongous AE threat. But then how often does that happen?
The alternative - IMO - is Hungering Cold. It is extremely rarely useful just as is Deathchill, but at least when it is useful it provides a unique mechanic which cannot be matched, unless you actually bought Chillblains and glyph-HB into a group. Brings me to the second problem with it, it needs to be glyphed to be useful.
So it's a decision which ain't an easy one. If you can spare the slot I'd definitely go for HC and glyph it, since it will eventually end up being the button which saves you, your group or your raid. If you can't spare the glyph slot, Deathchill is a better choice, as rarely as you'll end up noticing it.
The ultimate answer is ofc Deathchill + Chillblains + Glyphed HB, but if you got that many points spare I envy you. :P
-- (The Death of Rats, Terry Pratchett, Soul Music)