Personally, I'd have gone for a mix. Hammering out enough of a hard timeline to make for a cohesive universe is a good idea no matter how you slice it. But needing to start Clark as far back as the 1930s is a is something that wasn't completely need (even though I'm totally good with and even in favor of the general idea).
A timeskip similar to how the Legion did it would've totally worked (and still could work). Nail down the ages of everyone that seems like they should be in their late 40s/early 50s and simply skip forward 10 or so years forward to where they're now comfortably in their middle age and Dick's gen is in their late 30s to early 40s.
That would've left it so Jon and Damian were in their very early 20s. As a bonus you make it so Jon joins a very young Legion at age 11 to 13 (while they're like 13 or 14 or something), and the Legion then has 10 years worth of room to tell stories basically forever, and the age up never actually goes down so people aren't bitching about that. Like, he'd literally spend the summer with Jor-El, get trapped on Earth-3 for like a month, and then come back on like his 13th birthday and found the United Planets on his birthday.
Keep the Wonder Woman being the first superhero and forming the JSA thing.
I don't think that's actually true, and I think people are getting too stuck on the timeline itself. The fact of the matter is that 5G would've basically had the idea draw for new readers as the New 52 because the point of it is ultimately the present day. That's why it's called 5G aka Generation 5. It's about that generation, and through them new fans connect. The world would've also been so new and changed that it may as well have been a reimagining from scratch.5G really would only appeal to the die hard canon scholars and feel like HW to everyone else.
The nerd/hardcore crowd would've gotten their fix doing all the deep dive homework that's there if you want it but not at all required to read the Gen 5 stuff-- which is the point. Again, it's like getting into Lord of The Rings and some people do the deep dives into the worldbuilding to find out the history of the world, and some people are just their for the present day story that functions as a relatively self contained jumping off point.
Once you take into account the fact that DiDio kept saying that the stories in Gen 2 (aka when Clark and Bruce started out as Superman and Batman) were still stories yet to be told, it's clear that he wanted to have a place to tell new never-before-seen stories about the older generation in their prime that would be for the more seasoned fans. He was trying to create a living breathing universe. He just needed to make his case better and be open to some edits.
Unfortunately it didn't work out, and the DCU is in one of the most half assed and directionless states I've ever seen it with Williamson doing the worst Grant Morrison impression I've ever seen while they literally regress back into past stories like Flashpoint and Death of Superman but "bigger and now it's the whole JLA". This is what a writer and company look like when they aren't willing to commit to anything other than just getting by. The D student of creativity and conviction.