Most of those damage reduction talents are at 51 points, and are the designated "pvp" talents. Guardian Spirit is a pvp talent. Dispersion is a pvp talent. Etc.. Healing the target for 10% of their health when it dies ('preventing death') really isn't going to save a tank if they're spiking that badly. Pain Suppression might, if you're deep Disc, but I'm not seeing the utility of Guardian Spirit ... yet.
The comparison between IHC and Borrowed Time is actually a good one, since those two talents define your play style with the two specs. If you go deep holy, IHC means every 7 or so casts, you get a ~ 1.4 second absolutely free max-rank GHeal. You can follow this with 2 hasted regular GHeals at the same speed, but costing mana. Your HpS will be extremely high from the constant haste procs, your mana will be doing fine because 1 in 7 casts (roughly) is free, and you have Serendipity if you overheal.
On the other side of the coin, if you go deep Disc, you get access to extremely high-absorption PW:S casts which are 1.0 second GCD and that effectively cost you 0 mana, assuming they absorb full damage. Your GHeals will heal for a lot less (no Spiritual Healing, no Empowered Healing, no Test of Faith), but if you happen to crit you get most or all of the difference back from Divine Aegis.
When I did the math assuming 2600, 2800 and 3000 HSE and a *9%* Grace, deep holy still healed for quite a bit more per cast, several hundred points of healing at minimum. You have to make up that difference from the PW:S, but as you showed, that only heals for ~ 4k HpS.
In deep holy, assuming the holy conc procs, and assuming worst case of a proc every 10 casts, and using max-rank numbers as you listed, I could sustain theoretical HpS of over 4500 HpS. Yes, I could go deep Disc and cast a 4k shield, but I can easily sustain higher pure healing throughput from straight-up GHeal in Holy.
At least they are comparable. Once someone gets into Beta, we can start actually testing throughput and looking at the spell details for all of the various ranks, and get a feel for how Grace will effect things.