That's not why Atomium got 3.5/5. It got that rating because it's main ability can only be used weekly, and most Wonder abilities reset daily, so you can use your Wonder abilities an extra time per week. Nothing too special, as it's a gimmick. If it got buffed to 3 days, and it decreased University costs by 10%, then maybe it would get the 5 stars. I mean you're already getting 30% off the cost and time just by completing Musa and Hiawatha, which is just enough in my opinion. I guess I forgot to mention that all the economic wonders become nearly useless upon completing whatever. But do realize that it's in the economic wonder's nature. They're supposed to help you along the way. If it managed to help you along the way, then it did its job. It got the 5/5 stars, and these wonders are quite likely to do so (except, you know, Temple of Tikal and Pyramids, as their ratings are lower). They're not going to help you on defense or offense (except maybe Sydney Opera House or even... Atomium).Respectfully disagree with many of these assessments. If Atomium gets 3/5 because "top players have probably completed those University researches," then Stonehenge, Pyramids, Notre Dame, etc gets 0/5 since many of these players also have max walls and likely fully upgraded bases. Naturally, with the addition of additional ages and buildings/walls to upgrade, there will be additional University researches to upgrade as well. Also I war against these top alliances, while their maxed bases do not have the Atomium, many of those lv 210s-230s in the same alliances do have this wonder. I can assure you none of them have some of those 5/5 wonders you mentioned. It's more popular than you think. Honestly, you can't randomly apply one criteria to one wonder and negate that same criteria for other wonders as well.
As hinted, wonders are highly dependent on the Age of the player. For example, everything outside of Acropolis is nearly useless for a late Atomic player, the defensive nature of Colosseum becomes more and more minuscule starting Enlightenment Age, etc.