For me, being able to step up and face failure is just as inspiring as it is real. The original characters when from mythic icons to highly relatable people. And that's far more important to me, because we still have the Original Trilogy. Those events still have significance, still have impact, and are not diminished by future failure. At least, in my mind, they shouldn't be.
On a larger note, the PT had addressed this earlier. In the OT, the Jedi were highly romanticized, and we longed for them to come back, and celebrated Luke's famous "I am a Jedi, like my father before me." But, in the PT, the reality was much messier. We saw the Jedi with flaws, and failures, and outright terrible choices. We saw Obi-Wan and Yoda take a very cowardly reaction to their failure and run away.
If the ST follows anything, it follows a theme already set in the PT.
Possibly three of us
I think in the OT they went from mostly relatable people to mythic status and it's the myths that the Disney sequels want to tarnish, but that doesn't make the sequel version of the OT heroes more relatable to me, it just makes them pitiful. In the OT Han was just a shady smuggler, Luke a farm boy with stars in his eyes, and Leia was a political leader and rebel fighting a war whose outcome was far from certain. Leia was the closest at the start of the OT to mythic status, owing that she was a princess and a young senator in the Imperial Senate as well as Rebel leader. But even with all her titles and talents the OT presented her with challenges that created enough suspense because we didn't know how it would turn out. And the OT addressed failure and showed how characters dealt with it.
As you pointed out, failure was a major theme in the PT and pretty much everyone failed in that trilogy. Even Palpatine didn't get the pristine apprentice he wanted. He had to settle for the mangled Vader. Though the PT didn't spend much time IMO showing people deal, or certainly overcoming, their failures since it could rest on the OT.
I disagree that Obi-Wan and Yoda were cowardly compared to Luke and Han in the sequels. In the PT, Yoda and Obi-Wan were facing the rise of the Empire, a legion of soldiers programmed to kill them, and a skillful Palpatine that had turned public opinion against the Jedi and convinced people they were traitors. Plus, Obi-Wan had to protect young Luke, and Yoda went to contemplate and learn a deeper meaning of the Force. With sequel Han, he has a bad seed son which presumably drove a wedge between him and Leia so Han just left to go running around the galaxy, losing his beloved Falcon somewhere along the way and mostly giving up even on finding it. Luke shut himself off from the Force and went into self-exile to die, which doesn't make sense since he created a map that would show where he was if he was really so hellbent on sulking and self-pitying himself to death. Unlike Obi-Wan there was no one Luke was protecting, there was no potential for the future, for the return of the Jedi. Luke wanted the Jedi to end because of his own personal screw up, his ego became more important than the billions or trillions of people counting on him. He turned his back on the galaxy, on his sister, on his friends, on his nephew, and said screw the galaxy. Obi-Wan had a charge to keep and Yoda grew in the Force, but Luke didn't. His final stand, while well shot, was ultimately a waste of time since the Resistance was all but wiped out. Plus, it felt dumb that Rey didn't tell him anything that he didn't already know that he needed to do, so for him to pick that moment to make his stand when he could've struck earlier before the First Order, Snoke, or Ben had grown so strong, or if he had even just lent his presence and military/warrior mind to the Resistance cause without calling on the Force or even picking up a lightsaber again, he could've saved more lives. But this 'Luke' (to me, he's Jake Skywalker) had to be a sad sack because it fit the story Rian Johnson wanted to tell, his previous characterization be damned because Johnson wanted that version of Luke. And Johnson being the director, imbued with authority by Disney, had a right to put his vision on the screen, just as I the consumer and fan have a right to critique it.
And with failure and/or how we deal with it already being covered in the PT and OT, I'm not giving any major points to this theme being revisited in the sequels. Especially in how they threw dirt on the reputations of the OT heroes. If you wanted to have Luke fight and lose, I can accept that, but him running away felt completely opposite of his strong belief in the redemptive nature in the heart of Darth Vader. He risked all to redeem his father. I couldn't see him not doing the same for Ben.