This is Tengulf, my little DK. and I'm going to shove her into simcraft and generate some data to answer your questions, now i'm not particularly hot on DK maths so I'm leaving her APL as the default one and have her face the T16N10 boss, since hopefully that will provide an adequate compromise between hitting her too hard (and thus favouring raw Survival) and wet noodling her (which would over estimate the value of DPS stats). The results are only as accurate as the boss model and APL model your situation.
With her default stats (heavy mastery) she gets;
286725 dps, 109023 dtps, 182439 hps (98990 aps), 140.1k TMI, 59.05% BS uptime (335k), 11.5RPS
if we then where to swap 10k mastery into Parry she gets;
323600 dps, 121697 dtps, 151663 hps (61182 aps), 150.2k TMI, 44.13% BS uptime(302K), 12RPS
and then if we where to swap 10k mastery into haste instead
311504 dps, 136170 dtps, 170030 hps (71960 aps), 152.2k TMI, 43. 11. BS uptime(305k), 11.3RPS
25k iterations of each.
Now according to these results you can see that there's not much difference between Haste and Parry, Haste takes more damage, but counters that with more self-healing,but overall is slightly spikier and about 4% behind on DPS. Mastery, of course, is quite behind on DPS, but minimises Damage taken, TMI, whilst maximising self healing an Blood shield uptime.
so why did haste perform so poorly?
Firstly, the number of Deathstrikes is not really important, the timing of them is important, so whilst haste does increase the number of deathstrikes, deathstriking just to keep runes rolling doesn't really increase survivability.
Secondly, Parry haste, a mostly forgotten mechanic, when you parry an attack the swing time on your next white swing is reduced by 40%, this reduction cannot reduce swing time below 20% of the original swing time. tis ois why parry is preferable to dodge for DKs, regardless of diminishing returns. It allows you to double dip scent of blood stacks on a parry, since not only do you get a stack for the parry, but you accelerate your next stack melee hit
Thirdly, Most deathknights do not need that much haste to GCD cap, in the mastery build i had 4% waiting time, in the parry build only 2%, the haste build had negligible waiting time. Once GCD locked you aren't gaining that much since you're now time limited, an increase in DS means less time for everything else, so whislt you might have more RP to dump, it means you have less time for everything else; you're going to run into situations where you're RP capped and you have a rune pair recharged, do you DS and waste up to 20 runic power? or do you RS and leave your runes not recharging for a full second? what if you have a crimson scourge proc at that time? do you risk clipping it? whatever you do you're gonna end up wasting something.
So why is haste so popular? taunt swaps. almost all the reasons haste sucks go away, or are largely diminished when you're not actually tanking anything, if you're not getting hit you don't get riposte, which decimates parry DPS value, you don't get and stacks of SoB from parrying, nor do you get parry hasted. Parrys value is based on you getting attacked if you're not being attacked parry is worthless.