The difference is the future movies need to stand by the change. Vader as Luke’s father isn’t contradicted by ROTJ. Luke and Leia as sisters was pulled in last minute but if you go back it isn’t that bad, as Luke and Leia never show romantic feelings or something. If it were so obviously a later change it would have been a bad twist. Same for Anakin, his motivation actually algins better imo with the love established in AOTC.
The ST though honestly feels like Abrams and Johnson wrestling for control over the story. TLJ at least tries to build on TFA even if many of the twists toe the line, I’d say they work. TROS abandons any regard of plausibility.
Imagine if ROTJ revealed the following. Vader lied to Luke and the twist was just for shock value, REALLY Luke’s father was a heroic Jedi Knight. All the emotional opportunities and arcs setup by ESB? Nevermind.
The Empire that has been steadily built up as the big bad is nothing more than a shill for the Yuuzhan Vong, who arrive with no explanation and midway through kill the Emperor. The threat level of the Empire last movie was literally based around? Nevermind.
Han suddenly has no agency… wait nvm ROTJ already had that. All his arc as a smuggler slowing turning good skipped over to the end, where he can be a flat character meant to drive plot.
The Vong seem to contradict everything Yoda told us about the force but no one addresses it. So all of Yoda teachings? Nevermind.
In the end, Luke wins and goes back to Tatooine where he takes up the name “Lars” in honor of his aunt and uncle for whatever reason. The entire point of Luke trying to move away from Tatooine and see the galaxy? Nevermind.
This contradicts everything ANH and ESB were setting up. Maybe a few of these could have worked, had it been properly developed, but using TROS as a model none of them would be and it’d all make no sense.