The original trilogy (OT) felt majorly disconnected from the prequels plot-wise for a long time, ESPECIALLY Vader. I feel like Kenobi, for all its flaws, has connected the OT and the prequels pretty well.
Re-watching Vader in the OT in light of Kenobi, OT Vader feels like he is a continuation of his prequel character in a way he didn’t before. Kenobi has done what the prequels, by themselves, failed to do adequately: show Anakin become Darth Vader and make the OT Vader make MORE sense, not less.
It just didn’t make sense that Vader would be so calm on the Death Star in A New Hope if it was his first meeting with Kenobi since Mustafar. But re-watching the A New Hope Vader/Kenobi duel in light of their duel in Kenobi, it just felt right. Vader has had years to prepare for his reunion with his master and has already had ample opportunity to vent in their previous post-Mustafar clashes, as seen in Kenobi.
Similarly, in Return of the Jedi, when Luke tries to convince Vader to join him and Vader says, “Obi-wan once thought as you did,” it made NO SENSE if Vader’s last interaction with Obi-wan was Mustafar. But, in light of Kenobi, it totally works: Obi-wan did, indeed, try to redeem full-on, half-machine, pretty far-gone evil Vader.
Kenobi makes it much easier to see Anakin in the OT Vader and makes the prequels work AS PREQUELS in a way they didn’t before.
I personally think the OT stand on their own as masterpieces and I’m pretty sure I’ll have my kids watch the OT, by themselves, first before letting them dive into the rest of the Star Wars universe if they so choose. But I’m glad that Kenobi exists, for all its flaws, because the prequels felt incomplete beforehand. Now, the prequels plus Kenobi plus the OT more or less satisfactorily tells the Anakin/Darth Vader story as a single, coherent plot. For that, Kenobi more than justifies its existence.