It was both, though I don't think they ever really commented much on the roaming aspect outside a brief comparison to Odin (who was called the roaming Primal, though he doesn't do a whole lot of that with his static spawn points...).
Basically the plan was; We'd be able to fight a Primal as a Free Company, we'd do something in order to charge it up, then we'd be able to unleash, during which the weather would change, indicating to the server that the Free Company had summoned the Primal, and that there was a new chance to try and claim it. They never really commented on how it would spawn, just that there would be one version (so one Ifrit, one Garuda, etc.) per server.
I know it's a thing, I said it wouldn't be much of an issue if they put proper workarounds in place. This is mostly because they've always talked about roaming Primals as something we'd effectively capture and then use. Right off the bat, they can limit a Free Company to a single Primal; If you got Ifrit, you can't claim Shiva or Ramuh. One of the mechanics they specifically mentioned was the weather changing, to let the entire server know that Ifrit has been summoned. A small group then, cannot monopolize a Primal, since they'd be finishing up whatever they summoned Ifrit on while Ifrit is out ready to be claimed again. For larger groups they could quite easily limit your ability to have one sub-group summon while another claims, they could literally just say "You had Ifrit this week, so you get no Primal next week".
Were this like the old school world bosses, where a group claims it, kills it, gets some loot, then waits days for its respawn window to reopen, then monopolization would be an issue. That isn't what they've suggested though, the "loot" from the roaming Primals was always the ability to summon them, and since that is tied to Free Companies, they can quite easily limit monopolization there. The bigger issue, like I said, is the utter lack of content to use them on. If you can use them on instanced content, then that is just simply unbalanced. Being open world content, they should be used solely for open world content, yet sadly we've yet to see the bigger, better version of Hamlet Defense. They even said the whole world/server would be involved in the summoning of them, and if I'm summoning Ramuh to get an easy A4S clear, that simply isn't true. We need open world content where summoning these can feel epic, and making short work of an S Rank or FATE boss really doesn't seem epic to me... With that in mind, monopolization actually becomes even less of an issue. Yeah it sucks that that group gets a Primal each week, but if they're using it to turn the tide in a Besieged/Campaign style event? The entire server is benefiting from them summoning it, rather than it solely being for their benefit.