Summed it up well. There is really no need to use the "Robin" nod because the identity isn't diffused between multiple characters. There would be no precedent for it. There would be no Robin legacy where "Robin" is looked at as a position rather than an individual character.
Also you have the Teen Titans cartoon too that is a combination between Dick and Tim. That Robin has Dick's history, but is designed and molded after Tim in the sense that he is the 3rd Robin of that universe I believe along with using Tim's design.
Limit him how? We know the stories that were told with Dick in that time period between crisis and the Batman office using him more again. They were not very good. The most memorable stories with Dick over that era were ones that tied him back to the Batman franchise anyway. Having Dick be stuck in that Titans book that would collapse over the next decade with a less iconic identity did not help the character in the long run. Then you have the Batman writers over that same time period redefined the Batman franchise and turned it from one that was selling half of what the NTT book was to becoming DC's flagship franchise far outpacing the Titans. Dick missing out on that era hurt the character in the long run. Those Titans stories as I’ve said before are completely irrelevant now, so it just wasn’t worth it, imo.
You are looking at the stories as they happened and trying to figure out how Dick as he was back then would fit into them, which doesn't make sense. It's more about how everything around these sorties and books would have changed if there was no Robin legacy and it was just Dick Grayson. The YJ book happened because DC probably wanted a new young hero team with how much of a mess the Titans became and with them getting too old. Plus the success Marvel was having with their young characters might have factored into it too. So a YJ book would have still happened probably, but it would have been different to what we got. Maybe it would be more of a young adult book if Dick wasn’t deaged, or if he was deaged, which is something that has happened to the character multiple times over his history anyway, then it might have been about proper teenagers like Tim’s book. But then that only lasted a handful of years before they moved Tim's YJ team over to the Titans anyway with adult characters.
I’m not saying it would have been as iconic, but a version of it probably would have still happened. Writers have these story ideas in their heads for a long time usually and they go through constant changes based on what they can or can’t do. Maybe Dick would have even died and not return for years. Who knows, but the point is that Dick would have been more involved in that era of Batman stories that basically serve as the foundation for most modern Batman stories now.
Like maybe even a Knighfall story plays out differently where if Dick isn’t stuck in the Titans he takes on the Batman mantle sooner and defeats Bane instead of Azrael. Where that landmark Batman #500 issue is Dick wearing the Batman costume facing off against Bane and it becomes a seminal moment in Dick’s long history. I’m obviously looking at it from an optimistic pov, but who knows what would have changed in the end. I do know what we ended up with, and while it isn’t the worst outcome since Nightwing is successful enough to not be a failure obviously, but I don’t Dick’s character ended up with the best outcome after giving up the Robin identity.
Robin is a legacy identity and a position multiple characters have held. So Nolan having this “Robin” character was a nod to the Robin legacy and position rather than the individual character, but if Dick is the only Robin and there is no Robin legacy then this likely wouldn’t have been something that occurred to him to do. It would have just been Dick Grayson because that is who would be associated with Robin. Just like Bruce Wayne is associated with Batman.
The Boy Wonder title kind of died off a long time ago by the 80s. I think they stopped using it in 60s or earlier? I mean as someone mentioned Dick did already grow into an adult as Robin and continued to use the identity and work with Batman and even the JSA. So it isn't this outlandish idea when it had already been done before. What Dick was back then as an adult Robin is basically what Nightwing is now, but just with a lesser identity in Nightwing as opposed to Robin.
I mean Nightwing already plays second to Batman. Look at any larger Nightwing story in the past decade. It’s all Batman telling Nightwing what to do and then Nightwing doing it, or Nightwing getting used as bait to prop up Batman’s own story by either getting captured or injured. To me it feels like he has even less freedom than Robin given Robin is the character more associated with the Titans over Nightwing in DC’s eyes.
But for Nightwing to function it had to be positioned behind both Batman and Robin. It has more obstacles in its path for relevancy which will always limit it. Actually it has 3 things it needs. You have to have Batman, Robin, and also the Titans. Nightwing has done well given all the things working against it, but it isn’t in a great position to be marketed to the masses because of all this, imo.