I'm pretty sure shutting down DC travel would just kill Dynamis outright as people realize they're trapped on a dead data center with no hope for growth, at which point they proceed to mass-transfer away because having a house isn't worth 30+ minute queue times (if anything pops at all). Subsequently, every would-be new player would just delete and re-roll elsewhere before they got too far ...assuming we even get new players anymore.
The first lockdown and Cosmic Exploration's failed projects being as they are have already shown that the harder Square-Enix tries to force people stay on Dynamis, the harder they try to escape it and those who remain suffer more for it. Even as things stand our marketboard prices jacked up significantly after Cosmic Exploration because a noticable chunk of our long-time gatherers and crafters refused to be "punished" any longer for staying here. You start making those who engage with the combat jobs feel the same way and you may as well just shut Dynamis down and give everyone left a free transfer out to select Aether/Primal/Crystal worlds.
At best, removing DC travel would help Primal and Crystal, because they already had sizable communities even before DC travel was a thing so they would be "returning to norm", and Crystal in particular was "seeded" during its creation with other populated worlds while Dynamis was left to build by its self from scratch.
And no, I seriously doubt Dynamis would have grown "just fine" even if DC travel hadn't been implemented at the same time. Case in point; Materia. Nobody there can travel out, and surprise surprise, it's even deader than Dynamis and that's DESPITE the fact that literally anyone from NA/EU/JP can voyage over there to help. One-way/zero DC travel is a death sentence now, not a cure.
The only other solution is to rotate around existing worlds within NA, so some Aether/Primal/Crystal worlds go into Dynamis while Dynamis worlds go back out to Aether/Primal/Crystal. But people hated when Square-Enix did this to create Crystal, which is why they didn't do it with Dynamis to begin with, and with "congestion" constantly keeping various worlds (and sometimes entire data centers) locked up, it not only wouldn't be easy for people to just transfer back to their preferred data center, but it STILL wouldn't salvage Dynamis because people would "ewww" and leave the first-chance they got because it doesn't magically become THE data center for raiding/RP/PVP just because Square-Enix forced a bunch of raiders/RPers/PVPers over there. We have a stigma and it's never going away.
Frankly, their biggest mistake was making Dynamis at all, as they grossly over-estimated how many of the new influx of players would actually stick around, and now the data center serves no real function and has a negative reputation. Hell, the 1,000,000 gil they give you can't even afford a house, and that's assuming you can find one here that hasn't been bought up by submarine bots already.