I don't agree. Luke could have been head of a small beginning of the new jedi order and stuck to his 'master' post at the temple or wherever, leaving the battle to the newbies. Han/Leia could still have been married and part of joining/starting the resistance was to try and get their son back. They could have been 'generals/admirals' or whatever responsible for 'the home office' so to speak and not the one's doing the fighting. Everyone's lives didn't have be destroyed to diminish their power for the sequels. That's ludicrous. No one expects the 60-70 year olds to be out on the front lines. They could be there, be positive, and not be the focal point. Easily.
Well, a few thoughts, then.
1. First, your problem (it would seem) is not specifically with Rian Johnson or TLJ, but rather with the overall direction of the sequel trilogy (with probably a goodly portion of that lying at JJ's feet, which I think is a fair criticism). I don't disagree that you could've taken a different approach to Luke, Han, and Leia. But I do think it would have created a
very different film series that probably wouldn't have characterized the new heroes as quite so heroic.
2. I think you're wrong that "nobody expects the 60-70 year olds to be out on the front lines. Put simply, I think the same folks who are bothered by the direction of the new films would be just as bothered if the OT characters hadn't gotten out and fought. I mean, look, there are rumors about ANOTHER Indiana Jones movie, in spite of the fact that Harrison Ford is going to be pushing 80 by the time that film is released. For better or worse, there seems to be an expectation among folks that these characters can keep on kicking ass forever. I think that's unrealistic, but clearly some folks out there disagree, or else nobody would've talked about Indy IV let alone Indy V, ya know?
3. I don't think they necessarily needed to put the OT heroes in the positions they were in starting in TFA, but I do think that you can't have them (1) being the focus of the story, or (2) sitting on the sidelines UNLESS they are doing so for big reasons. The central tragedy of Ben's fall to First Order essentially fractures the lives of the OT heroes and, if you accept that Ben would've fallen at all, I think it's actually pretty reasonable to have Luke wander off as a hermit, Han run from his grief across the star lanes, and Leia bury herself in another rebellion. Once you set it up so that Luke's nephew, Han and Leia's son, is not the
hero of the new films, but rather the
villain, then I think you end up with something reasonably close to what we have. In many respects, it's not that different to Anakin's fall and the impact that had on the heroes of the PT. Padme dies in childbirth. Obi-Wan and Yoda go into hiding. Everyone else dies, basically. (Yeah, I know Bail Organa and Mon Mothma found the rebellion, but they were barely in the PT films.) Finally, if you think the complaints about "Isn't this just ANH all over again?! They're just recycling the OT!" have been bad so far, imagine if Luke really HAD been the Obi-Wan stand-in here?
I said before, does anything about TFA, for example change one single bit if Han/Leia are happily married and han's out on another ship making a delivery to a reistance base (or on his was back) when the stolen falcon pops up on his radar? Nope. Not a bit. Short of dumping the stupid rathtar bit. Han still dies trying to turn his son back, but there's no character reversal to start things off as it's totally unnecessary.
Actually, I think it changes quite a bit. It changes the emotional stakes for those characters, and I think in many ways diminishes the tragedy of Ben's fall. Plus, it sets you up pretty easily for a "And then in the end Ben will be redeemed, just like Anakin was, and we'll have an Ewok dance party at the end." Regardless, I think the real difficulty was in bothering to include the OT heroes at all. There's no really good way to thread the needle that isn't incredibly derivative of what came before, or such a jarring change that people end up disappointed. And it really doesn't help that we had 30 years of the EU to ask people to completely hand-waive away as if it never happened. For the really hardcore fans, I think that was a
really heavy lift, and was probably impossible for some. I mean, people are still pissed that Pluto isn't a planet anymore.