In my opinion they had nothing to fear if we go off of the idea the Ori were not ascended yet, sure they didn't want war i understand this.
but here is another thing that i found odd, they stayed for a very long time before they decided to leave their galaxy once and for all, i understand they were trying to convince people to bring with them or convert them, but they buried their space ship in that mountain and lived under the boot of the Ori worshipers for who knows how long and i would assume they had Priors at the time who would enforce the worshipers, all their tech was suppressed, which meant they needed to hide all their advanced tech from being seen by the Priors and any of the followers who might tell the Priors what's up.
However if there were ascended Ori during this time, the Alterans would have something to fear, also one of the more modern day ascended beings mentions that the Ori never allowed more into the ascended fold and never shared their power with others, well how could he even know this detail if he ascended within the past 10,000 years and hasn't gone near the Ori galaxy during this time as the other ascended others were super afraid of the Ori and very passive of their impending doom.
I understand they had the capability back when they weren't ascended to have access to information that they could download into their brain via repository of knowledge devices, so maybe there was some kind of historical archive in these things, and maybe there were more of these things back in their day as well, so it's possible the archives could have possibly mentioned something.
I think it was Orlin who said that the Ori never share their power with other ascended beings, he turned out to be wrong as Adria mentions there were a great many who shared the power of the Ori before she took the mantle of their power.
But where did he come up with this information if they weren't already ascended when the original Alteran left that galaxy behind?
From what we understand about ascension via the ascended Alteran, they are not all seeing all knowing or even all powerful, they simply exist on a higher plane where they have more potential in what they can observe and learn from their environment.
When Vala and Daniel first meet with the Doci, when he has the Ori take possession of his body, the Ori explain that the Alteran shielded us somehow, which is an weird concept because after Daniel's conversation with this ascended Ori, a Prior is immediately seen walking through a milky way stargate, like did they probe Daniel's mind during this conversation?
i mean how else did they know where to get to the milky way galaxy and sending their Prior through the stargate no less?
There are just a lot of questions that the show doesn't really explain too well in some of the situations and the wiki also doesn't explain some of these things.
Like how did this religion even start to unfold and take over an entire galaxy of people that used to be united as one species of technological advanced people?
They must have been under some kind of oppression or decline that they could not fight or defeat with their tech, and typically people who are more of an science oriented people don't fall back on religion, unless something catastrophic takes place like a war or a famine where they have no hope in their capability to cure themselves.
I know the Alteran had issues with a sickness that killed people within the milky way galaxy, and i remember them attributing it back to the Ori for some reason, so this might have been why the majority of people were religious as they lost hope in their tech to cure themselves, but something had to of stopped the illness as this sickness wasn't an issue for the Alteran just before they left their home galaxy.
But somehow it followed them to the milky galaxy, also we don't know when this plague started effecting them as they built their empire on Dakara originally and built many astria porta or stargates, i'm assuming it was the first version of gates at this point.
Then they went to earth at this point and discovered that background microwave radiation trail in the universe, so after this they created many seed ships that were capable of running automated, then they built the destiny to follow that path and investigate that BMR trail.
Then shortly after that, they started building their second version of stargates and filled the entire milky way and it seems a few other solar systems outside as the asgard who were outside our solar system and had a few of these version of gates with them, then they advanced further and built themselves an entire city ship of Atlantis to research the Pegasus galaxy, however i assume they sent their seed ships first to populate every planet with a gate system to use.
Then i believe the plague hit as Atlantis was almost ready to embark on it's mission, which also served as a life boat and a way to save the ones who were not infected by the plague, so they stayed on Atlantis for some unknown period of time within Pegasus until they ran into the wraith or they created them? i might be confusing this with one of the damn novels because i can't remember if they created the wraith or not at the moment.
Anyway they created the replicators to help with the fight with the wraith as well as used them as tools to repair their city and other tech they had at their disposal, then the replicators turned against them and started ignoring their needs for some reason?.... i'm not sure, i cant remember why right now.
Then the Atlantians came to grips that they were losing this war and were running out of options so they decided to submerge their city under the sea and leave for the milky way even knowing that they would have to face the plague, they had to come up with a plan, i assume they already had some scientists who were researching cures and other ways of survival, we know during their time on Atlantis they came across a creature that was a massive black thing that absorbed power, we don't know what this creature was but i think MacKay mentioned it was related to their research of ascension and this could have been an experiment of theirs that lead to their understanding of how it was possible to ascend.
So when the Atlantians came back to the milky way they came up with a plan to ascend but they also had a plan to destroy all life within the milky way using the Dakara weapon and i would assume they set the device to turn on at a certain point in time, then activated all stargates at the same time when they sent this wave of energy to every planet to destroy all life in the galaxy, then the Dakara platform activated once again seeding every planet with new life.
Sorry this was so long, i kind of went off topic here, i do this when i'm sleepy and trying to figure something out while i type, it's a bad habit of mine, but it serves for good reading material when i eventually come back to fix my errors lol.