You missed the part where ROTJ's opening weekend was only 9% of its opening gross, and it was only $67.7M adjusted for the 3-day weekend, which is downright modest by today's standards. Sure, it may have set a record at the time, but that was highly atypical for a movie back then, it was still not a very front-loaded film (again, not even at half its lifetime gross after 30 days), and that record, even when adjusted for inflation, puts it at 234th place for all-time best opening weekends, bested by films like Troy, Scary Movie, and The Longest Yard, films not exactly know for record-shattering openings. Even if you added Memorial Day for the long weekend, it was at $89.7M adjusted, just shy of 12% its lifetime gross. Also, it's worth pointing out that the most front-loaded blockbusters of the 80s were, like ROTJ, all sequels to hit movies that were not very front-loaded at all. Ghostbusters II, Back to the Future Part II, Beverly Hills Cop 2, Lethal Weapon 2, Crocodile Dundee II, even The Temple of Doom and The Last Crusade to an extent. All vastly more front-loaded than their originals. But original films? E.T., Raiders of the Lost Ark, Back to the Future, Ghostbusters, Tootsie, Beverly Hills Cop, and Top Gun were among the best-performing films of the decade, and they were all relative slow burners that stayed in cinemas for at least half a year or more and took several months to reach ~90% of their lifetime gross.
Put short, the increased front-loading of movies wasn't something that suddenly happened overnight in cinemas in the early 80s. The idea that some massive sea change in viewing habits by 1980 was what kept Empire from grossing what A New Hope did is entirely without merit or any supporting evidence. Those supposed changes in viewing habits after 1977 didn't keep E.T. (1982) or Titanic (1997) from netting well over a billion dollars adjusted gross in their original theatrical runs (and even Box Office Mojo has The Force Awakens at over a billion adjusted now). It takes a rare special movie to pull those kind of ticket sales, and The Empire Strikes Back and Return of the Jedi were not those movies.
Star Wars was brand new in 1997, limited in release, and took a ton of time and word of mouth to propel it to blockbuster status, but once it did it became a major pop culture phenomenon. It was something new, something fresh, something exciting, but it wasn't an overnight hit. But it ended up becoming the second highest-grossing film ever adjusted domestically. And neither ESB nor ROTJ were going to replicate that level of success, even if they had a full year. They didn't have the excuse of home video or TV broadcasts to drag them down a few months after premiering, either. They simply don't have any excuse for failing to draw the same kind of ticket sales ANH did. Not as many people felt they were worth seeing, or at least not multiple times, and they didn't have the same novelty that ANH did. And after three times of a Star Wars trilogy having a huge first entry and the follow-ups not doing as well, I think it's safe to say that we're seeing a pattern. Hell, when the original trilogy was re-released in 1997 as Special Editions, A New Hope grossed more than Empire and Jedi combined. Why? What was ESB and ROTJ's excuses then?
Personally, I think you and others who share your views simply feel the need to downplay TLJ's box office figures in order to support your narrative that the movie is objectively some sort of cinematic abomination. The very idea that film could be anything other than a financial disappointment is outright abhorrent to those who hated the film. You want the film to be viewed as a disappointment, because you hate it. And honestly, I haven't seen such a gross overreaction to a movie in my entire life. You know why so many people look down on geek culture? Petulant rage fits over movies not playing out like you wanted are almost certainly one reason why. Most people just want to enjoy a good movie (and it was good), and aren't going to engage in some asinine boycott and demanding producer resignations and director terminations because Luke Skywalker wasn't treated like Jesus Christ. The 30 Minutes Hate videos on YouTube are for a small niche of disgruntled Star Wars fans that have made this fanbase incredibly toxic, even more so than usual. Rian Johnson and Kathleen Kennedy did not rape anyone's childhoods. Is it too much to ask for Star Wars fans to grow up and get a grip? Apparently so.
I wish I could frame this.