When the fastest timed science games include them, then I will look again.
The question is how much production does it take to make something that makes more production and what is the value of using that earlier production for something more useful.
I can get sub 200 SV’s fairly regularly and my cities rarely have more than 60 production. I do not rely on those 60 production cities to get me there faster because 7 charge workers are far faster.
The fact that the fastest science games (an incredibly low sample size!) don't have IZ is pretty meaningless in and of itself. It is more telling about individual player's style and preferences than it is about optimal play. Most of them likely don't feature founding a religion, or late-game pillage wars (I assume), but those things can definitely speed up a SV regardless. They're just not very common occurances, doesn't mean they aren't viable.
Realistically, if you have really high BPT you can skip some Eurekahs without crippling yourself, in fact it could probably speed up your game. In these games it seems like building IZs is not really worth it, since you will not be getting much out of the Eurekahs anyways.
In a game where there is 0 or 1 scientific CS and your BPT is generally bad while your CPT or GPT is strong, suddenly not only is skipping Eurekahs much worse, but also the Eurekah is worth more in and of itself, because getting the Eurekah will actually speed up tech progression (as opposed to high BPT games where you have to
delay techs to get Eurekahs, which is counterintuitive).
That is why I rarely make generalist statements. Yes, some games you don't get IZs. In others you don't get HS, in yet others you get few TS. None of that is a plausible argument for not building IZ in general, and for skipping essentially 3 Eurekahs, which is a big deal. I'm convinced that one could reach optimal win times even with building IZ.
What's the fastest science game currently, like 170 on standard settings and 160 on any settings? I already came pretty close to that just playing my "suboptimal" strat of 4 IZ with mausoleum and angkor (wonders that most players would skip for "optimal/fast" games), if I find a good map in the future I will try just how fast I can win (HOF rules) with 3 or 4 IZ
some of my thoughts regarding IZ:
IZ are almost bad by design. Districts and district buildings are so good because they give you lots of global yields. Science, Culture, Gold and Faith are ALL global yields. A satellite city which is useless for central production can contribute to your global research, or can make you rushbuy buildings/workers via gold and faith. Production and food however only count for the specific city they are in. Local yields are always less useful in game where you have 20+ cities. That is one reason why IZs are bad compared to buildings with global yields. The only global yield of IZs are GE points.
IZs are also bad because the buildings are horrible. Workshops are imho not even worth building and I only get them because they are a Eurekah/requirement for Factories. Even factories are not that great currently. However, production in your spaceport cities is very valuable, because it has lots of modifiers for space projects. And production is not easy to come by outside of TR with allies.
Lastly, IZs are bad because building production is often not what you want to do. Especially in fast games. The longer the games, the more you get out of your built production. But the problem with building IZs is that building/buying workers usually gives you more hammers. And other districts, again, provide global yields. Global yields are very hard to come by via tile improvements, but hammers and food are not.
Still, with all this being said, building Workshops is good just for the Eurekah. In some games shaving 3 turns off of Indu means shaving 3 turns off of your win. Which is very significant. Of course, opportunity cost is a thing, but IZs are frequently heavily discounted in my games.