That's because Disc Priests have other spells on cooldowns (note: these spells are limited by their CDs) that they cast in between PW:S. If you actually did the math, you'd realize that in those logs, the Disc Priest was casting a PW:S every 4-5 seconds.
Also, you're kind of stating the obvious. While PoH cannot be used before damage occurs for obvious reasons, the reverse isn't true for PW:S. The main flaw with your argument is that you haven't accounted for the fact that every boss this tier has mechanics that either do pulsing damage or damage for x seconds.
Look at these logs - the ratio of PW:S to PoH is so clearly skewed in PW:S favour.
Do you think heavy PW:S has much thought or effort associated with it? It has none of the cast time, range limitations or even overhealing consideration of most spells. It's the exact definition of mindless, regardless of your arguments over what spamming construes.
Of course PoH+SS is better. That's the only reason you don't see much heavier PW:S usage. Still, it has to be said that PoH+SS has a cast time/movement restriction unlike PW:S.
Under heavy raid damage, your typical Disc Priest is going to use PW:S to maximize BT usage and PoH between these casts for efficiency. That's fine, it's not an issue. The issue arises when PW:S starts doing similar HPS as PoH under ideal conditions for PoH, as it means that PW:S surpasses PoH as a raid healing tool under almost every circumstance. Go have a look at specific portions of logs (i.e. the Iron Qon log), and you'd see that PoH's overhealing isn't negligible even under heavy raid damage.
H-Jin'rokh, H-Council, H-Durumu, H-Primordius, H-Consorts and H-Lei Shen all see heavy PW:S usage beyond shielding the tanks or people with debuffs. You can harp on semantics if you want, but it doesn't change the issue that Disc's can rely heavily on blind PW:S usage and still do exceedingly well.
What exactly construes appropriately geared? The mana costs of spells remain static, which means that we've long past the gear threshold to sustain PW:S usage this tier, and it's going to become even more sustainable next tier at this current rate of gear inflation.
You can argue that PW:S isn't too strong based on the proportion of healing it makes up, but I'd disagree, because SS and Atonement are equally big problems too. I mean, look at Resto Druids/Shamans, Holy Priests and Monks - these healers are easily interchangeable and can fill each other's role with ease. Then you look at a Disc Priest's toolkit and you see such outliers in heals - PW:S, SS and Atonement are so unique and strong in their niche that it is a problem when it comes to balacing healers.
You can't possibly argue that a 180k average instant on-demand shield from PW:S isn't too strong, especially when you consider the single target equivalents from the other classes - all of which have a cast time and don't even come close to the numbers PW:S puts out. Then you have SS on a 1-min timer - it's bar none the strongest tool at addressing mechanics that do one-off damage on a >1min timer. No other class can lay claim to a skill that is that potent and on a 1-min timer too. And you have Atonement next - it's by far the best tool to spot heal the raid, is very efficient and spammable, and yet requires very little effort to utilize properly. This isn't even factoring in its ability to contribute damage. Heck, even DA is becoming really powerful with increasing crit levels, especially if you use it in conjunction with a Disc Priest geared heavily for Atonement (more Int/Crit, less Spirit).
Disc's numbers may be balanced in a 25-man, but that doesn't mean that the main trifecta in its toolkit isn't too strong for the kind of spells that they are. Disc's deficiencies in its raw healing toolkit should not be an excuse to keep Disc siutationally much more powerful than the other healers (Horridon, DA, Megaera, Ji-Kun, Primordius, even H-Lei Shen as no other healer comes close to what Disc can do for transitions/P3), especially since it's still very strong on fights that do favour raw healing.