The objective of game design is to make a good game. If you can double physics processing then you can have twice as many actors doing things "at standard" levels of computation. You can make the moves twice as nuanced, adding fidelity to the translation between input and execution by a factor of 2.
All of what you say is certainly useful from a technical perspective. But is any of that really the job of a game designer? It seems to me that such optimizations fall under the purview of software engineers and game engine developers. If a game designer is spending most of their time optimizing the back-end, they aren't actually designing games. What they are designing is game engines.
Don't get me wrong, designing solid, quality game engines is a very worthy endeavor, and the industry is much better off for having good engine developers. But it is not the same as game design. Engine development helps to empower designers, and has become a very important aspect of game development. But it cannot be equated with game design.
I don't see what difference it makes. Games are games. If I can do something that takes 40 hours and makes it a lot better then I'll do it. If I can take a different 40 to make it a little better, why would I do that instead, if I can only pick one?
"Optimizations" sell the idea short, as a word. HL2 has loading times. They are terrible, awful intrusions into the experience. They could have been removed. Bad design, bad tech. No engine can fix that problem, only the coders on the game.
I have a lot of tech experience. I know I can leverage it to compete with fidelity of modern games, then outpace them in other areas. My AIs can be richer. I can have online play that's faster, more complex, with more people. ...
Game design is not just creating rules on a page. It's taking whatever resources you have and leveraging them as best as you can to improve the player's experience. If you have artists, you should use them. If you have tech knowledge, you should use that. Any improvement is an improvement.
I could, for example, spend a lot of time designing a rich combat system. Easy to learn, forever to master; that kind of thing. That's what I'm doing, because that's one of my strong suits.
I could wait for someone to create a system then copy them. Or I could do the work myself and make the game better. Same thing with tech.
Also, good tech design, as with the HL2 example, the kind you get the most mileage out of, is intricately linked with the design itself. Certain operations run on the GPU better. If you understand that, and what sort of code would work well with it, then try to make a game who's calculations heavily fall in that area, you could do some incredible things. You could make a high-end game run on a mid-range computer, increasing your player base.
The designer's job is to provide experiences to the player, through games. However he does that is totally irrelevant. All there is is the player. If you make decisions that create the best experience for him, you've won. Anytime you don't do that you've made a mistake. That which falls into the purview of designers, and that which doesn't, is game- and team-dependent.
I don't understand where the hate for tech comes from. It's one more piece of the puzzle. It's not like caring about tech marginalizes the other areas of design.
Each to his own, and all that.