It is very rare these days that someone outside the core team is so helpful to them as in this post. Most outside core would be just as happy to see core fade away instead of being so very helpful as TB is being here, albeit TB was masterfully trolled by GM into doing GM's job for him, it is just as likely that GM's ego or outside incentives will prevent him from taking any of this helpful advice to heart.
"Helpful..." That is an interesting interpretation of Troll's bashing, trash-talking approach.
GM shoots Bitcoin in the leg, TB shows him the wound, the blood, the gunpowder marks on his hand and hands him the surgical kit.
Satoshi put in the "silly" double hashing that Troll is calling "amateur," not Greg. According to
https://crypto.stackexchange.com/questions/779/hashing-or-encrypting-twice-to-increase-security, double-hashing was suggested in a well-known cryptography book of the time. We can debate whether it is really effective or not, but it's been there from the beginning. Not only that, but it's already pretty fast, and removing it would require not just a hard fork, but (according to my possibly wrong understanding) special handling to determine whether addresses, etc. were originally hashed once or twice... a logistical and coding nightmare, just to save a few nanoseconds.
As for the optimization Troll suggested, perhaps it would be useful. If I were a Core dev, I might even file this away on my backlog as something to look into.
But no, it's not on any critical path yet because the CPU is not a serious bottleneck. (Come on, people are running it on their Raspberry Pi's after all, whether you think that is a good idea or not!) Among the entire universe of possible optimizations, bug fixes, and features the Core dev team has to do, they may not have time to get around to your favorite one.
I get it, Troll is a self-proclaimed close-to-the-metal ninja coder. This makes him very useful in his niche, and his advice could be taken if it is truly not just trolling. But when you're very intimate with hammers, every problem starts to look like a nail, and you wonder why other coders don't just do as you would do in their place. A broader perspective may turn up some valid reasons.