I don't think she's short-sighted and narrow-minded - heck, especially not narrow-minded, how many tanks do you know that even consider haste when listing threat stats? - as much as possibly a bit misinformed. Let's see what a DST actually does for tanking before pointing fingers, at least...
I did a few quick approximations in the warrior TPS sheet (
moo) and got the benefit of a DTS at around 30-40 TPS (8% average haste - i.e. 15 seconds uptime/minute - and ~450 TPS from autoattack & HS before haste). That's comparable to about 3%-4% to hit (50ish rating, I think?) or 150-200 block value, in a situation where you're in no way rage-limited. If my approximations are valid then DST is going to be better threat than Romulo's or the Autoblocker in those situations.
That approximation is likely off by 20% or so one way or another but I'm fairly comfortable in saying that your bidding tank has a valid point: haste rating is a good warrior threat stat when HS-spamming. However, the fact of the matter is that if you've got the rage to HS-spam in the first place then you're A) likely not producing insufficient threat and B) taking sufficient damage that you should probably be using a regular tanking trinket instead of a threat trinket. Add to that the fact that the Dragonspine such a
massive upgrade for your physical dps and I very much agree that it's not justified for such a niche application. It's good thinking on the tank's part to consider it in the first place, but she should perhaps have thought it through a little bit further and discussed it with the dps before bidding.