Look, it's such an easy solution, I'm amazed that I never thought of it earlier.
DC's curse, all along, has been near-instant buyer's remorse each time they do some reboot/relaunch. And nowhere has that been more evident with the Legion Of Super-Heroes.
There were easy ways to deal with this, of course. Ignore it. Use the old "all records of this era were lost" trope along with the "Crisis left our memories fuzzy" excuse (which works well enough for the Rebirth nonsense). Find a convenient substitute to inspire the Legion and/or participate in their earlier adventures if you need to (Mon-El, Dev-Em, etc).
But no, someone decided that they just had to have Superboy back in the Legion history, because that cover of Adventure #247 was just too damn iconic or something. So just 7 issues into Byrne's run, Superboy was back--only now he had been from a "pocket universe" all along (not an alternate universe, which had clearly been banned by Crisis!), and that young Kal-El been a pawn of the Time Trapper all along, so he could make the Legion strong enough to thwart Mordru, so he could take over time himself later.
Oh, and it ended up not mattering after all, because a few years later they rebooted the Legion so there was again no Superboy in their history...and then a few more years later they did it AGAIN!! Bless you, DC! (Seriously, when are we going to get one of those "Marvel The Untold Story" books for DC?!? I'd pay big money for just a chapter on "What the hell was going on behind the scenes with the constant jerking back and forth on Superboy/Legion...")
And now that there is a Superboy again in the Rebirth thingie, and DC continues to pretend that they're serious about bringing the Legion back, well, we can go right back to the way things used to be--young Jon and his (still untold) adventures will turn out to have inspired the creation of the Legion...which is why they start every meeting by burning a house pet to death...
But there was then, and still is now, a better option--why can't they just decide that the Legion Of Super-Heroes was inspired by the Teen Titans?
That would also solve the difficulties of Superboy being so over-powered compared to the rest of the Legion. Because let's face it, like the Justice League animated series with Superman, Superboy was just in Legion fights to get knocked out early by kryptonite/magic/Darkseid so the reader would realize how tough the bad guy was while the rest of the team rallied to beat him.
I just don't see the point of frequently rebooting, if all you're going to do is go straight back to the old way...especially when there's was a perfectly good way to take things in a slightly different direction with some of the marvelous toys in your near-infinite toy box. Like the Titans...
Still, I should probably consider myself lucky. Somewhere, in the back on Dan DiDio's mind, is a version of the Legion inspired by Superboy-Prime...