I think some people already made a good point about Supergirl becoming a fulltime member of the Legion of Super-Heroes. That even makes more sense as she risks being made redundant by other characters, especially two other Superboys. It seemed ever since the New 52 and Rebirth came, there were two Superboys that writers didn’t really know what to do with.
Either they should’ve just stuck to Jon Kent or Conner. But they really can’t have both because objectively speaking either one of them has to go away even without dying. It’s like what we got with the first version of Jon Kent, Chris Kent and Superboy Prime. Either Conner or one of them have to go way. They really can’t have both.
Not to mention Supergirl also risks being made redundant by Wonder Woman and Starfire or her own doppelganger Power Girl. Making her a Legionnaire does help lessen things a lot but as somebody said, that seems too vainglorious. Especially if/when in the future she wouldn’t have much competition from other flybrick women.
The Legion of Super-Heroes already had problems with Superboy and Superboy-surrogates. The time when the original Superboy turned out to be fake or something when he died had Legion writers trying to seek substitutes whatever they can do about it. You’ve got Kent Shakespeare and even longtime member Mon-El being made to fill the gap.
(Same with Andromeda phoning in for Supergirl even when she actually encountered and ended up join the Legion again.)
It’s like if Superboy was supposed to be a young Superman, him having to constantly visit the futuristic Legion of Super-Heroes is going to cause a lot of continuity headaches. But trying to replace him with a surrogate’s going to be just as complicated. Not that having Supergirl join the Legion for good’s any better or worse but it’s much more practical this way.
I even think there’s always going to be trouble making Supergirl (and Superboy) stand out that they end up paralleling each other. Both of them were revealed to be clones of other people at some point or another, especially if/when editors were so strict in making Superman the only Kryptonian around. Both of them have joined the Legion and eventually Teen Titans.
Both of them had telekinesis. Both of them became Red Lanterns. Almost as if writers have little else to do with them. Another problem with Superboy’s that if he were to grow up, he’s going to be Superman. Supergirl should become Superwoman but at least she could become her own character more easily if Power Girl’s any indication.
There shouldn’t be any issues with her joining Legion for good. Similar things should also be said about other characters as well. Given the issues with making Wally West evil and nobody wanting Bart Allen to become Bar Torr, the only other solution and the hardest one’s to not only make both Barry, Wally and Bart actually age realistically (as possible) but also allow Bart to become his own man.
He could’ve gone on to become a detective or salesman really. I mean even if Barry Allen himself’s involved in forensics, Bart Allen becoming a detective’s a logical step and a better compromise really. (Part of the real reason why you don’t see Barry in the lab often’s because it’s going to be boring especially to people who never had experience in labs.)
Almost no other speedster became a detective for good. It would be just as vainglorious if because by becoming a detective, Bart Allen prefers to fight evil on his own terms instead of becoming the next Flash (as it happened before, it didn’t go well). Had he became the Flash, he’d just be another Flash. As a detective, he’s his own man (if only DC allowed him to actually mature).
Though I think the other problem’s that by then Bart Allen’s the character Tim Drake’s supposed to be even if it’s much more believable if it weren’t for the fact that children learn from their relatives’ behaviour by example. If Bart Allen’s especially close to Barry, it shouldn’t be a stretch for Bart to mimic and internalise that behaviour.
He’d even exceed Tim in detection really, much moreso had he been homeschooled. But then again another problem with superhero comics, though not unique to them to an extent, is that nobody wants the more iconic version usurped by a successor. Let alone allow the old ones to grow old. DC had no issue having Jay Garrick growing old. There shouldn’t be any issue with Barry Allen growing old too.
This should make Flash continuity much less iffy this way. Rather than retelling the same story all over again, why not have stories where Barry Allen does grow old and mentor Bart Allen around? JJBA’s sometimes not any better but it had no issue having Joseph and eventually Jotaro maturing and mentoring subsequent relatives.
Though that also necessitates having to genuinely make way for a new protagonist (JJBA’s arguably not any better either to some extent, especially with the current Josuke though he acts differently enough to be his own man). This is something that the Flash stories eventually did but that too got undone.
I’m not saying Barry Allen should remain dead as much as he probably has to become the new Jay Garrick should Bart Allen become an adult man. Joseph Joestar may’ve passed away by the time Jotaro started mentoring Giorno. Logically, Jay Garrick’s dead when Barry began mentoring the adult Bart. (Again I’m not saying Barry should die again.)
But it seems when it comes to intergenerational change, if Jojo’s Bizarre Adventures is any indication if you’re going to focus on the next generation they should still be made to stand out one way or another. Jolyne got wrongly imprisoned, Giorno was a gangster. Josuke got bullied, Jotaro was a delinquent. Johnny persisted in the race despite certain setbacks, Josuke II became a sailor.
This was already the case in the Flash stories where Barry was a forensic scientist and Wally became a mechanic. Bart Allen should’ve become a detective really. But then again that would mean doing something truly radical or at least distinctive enough to that character. The second Josuke became a sailor just as the second Yoshikage Kira was something of a good guy.
Not that Bart should become evil but there’s always a better way of making them grow up or change if superhero writers bothered with new influences.