Star Wars was in complete limbo after ROTS.
Star Wars was fine after RotS. TCW was doing very well. New video games were in production. The franchise would have kept on going as it has, just without the added hype of new movies, which Star Wars doesn’t need to be relevant.
The prequels are offensively bad to me, while the sequels feel more comforting. Safe, sure. It doesn’t ruin the OT with spoilers, ugly visuals, and terrible direction. It’s disposable, rather than damaging. It’s just a disposable sequel that doesn’t inject stupid lore.
The ugly visuals and bad direction of the PT don’t affect the OT (unless you mean the Special Editions, but those are a whole different issue). The spoilers are a problem for newcomers who start with the prequels, I suppose, but I wouldn’t call that “ruining the OT.” You can argue that Anakin’s portrayal in the prequels damaged Vader and his redemption, and I’ll agree with you on that.
I would definitely say that the ST also injected stupid lore, though. They did their best to be safe and derivative, but in doing so, they forced the post-RotJ lore into a creative dead end where everything has to lead to the First Order and to Palpatine on Exegol. It’s very difficult to work around that and make sense of that with new extended material, which will be hopelessly constrained and contorted to fit with the ST from here onward. The ST is like a lore black hole that everything now has to accommodate, whether it makes sense or not. The OT and PT expanded the universe, while the ST contracted it.