Gonna revise the list. It's going to include all independent modular main plot arcs.
6 Origins
Ostagar
Lothering
Redcliffe
Temple of Sacred Ashes
Circle Tower
Orzammar
Dalish Elves
Landsmeet
Endgame
Your DAI is combining Intro and Haven for some reason.
You're also discounting the Val Royeaux arc
There is also the Arbor Wilds quest as well as the well choice
So the list becomes:
Temple of Sacred Ashes Intro
Haven
Val Royeaux (serves to meet the Chantry and Templars) + Mage Redcliffe meeting (can be skipped).
Templars OR Mages
Haven Battle + Skyhold Intro
Wardens arc (including Nightmare)
Winter Palace
Arbor Wilds
Well consequence
Endgame
So here you have 10 "events" for Origins and 10 "events" for DAI.
There are 6 origins to fill the "Origin" slot, each taking up 1 hour at most, unless you RP walk everywhere.
Then you have the fact that Lothering can take between 5mins for those who ignore it completely, to up to 10mins for those who recruit Leliana and Sten, and up to 30mins for those who do the Chantry board quests efficiently. Lothering has almost zero main plot relevance so I'm being generous.
One can also note that the main quests in DAO are played simultaneously with side quests. This can artificially inflate the time spent on the main quest.
The biggest offender is the Dalish Camp, as the main story itself takes no more than 1 hour to complete if the side quests are ignored.
For comparison, the Exalted Plains Dalish Camp quests take as much if not more time to complete as they include the tomb quests accessed from Main Map and Emerald Graves.
Orzammar is the chunkiest quest of the bunch, but one can also argue that the time spent on the main quest is inflated by the Deep Roads exploration. Still, it's a significant 3-4 hours of content if played while ignoring side quests.
The Circle tower quest is shorter than the Warden quest, despite the former having a longer Fade sequence... There is also significantly less story in it as well.
Except for the Warden questline which is split into several areas, all of DA's main quests are "compact". The "side quests" that previously inflated DAO's main quests are now delegated to zone quests, keep quests, and other RP opportunities.
The divergence of the Origins in DAI occurs with the Mage/Templar quest.
You have two completely different questlines for the mages and templars in DAI each taking around 2-4 hours to complete.
Considering that this choice also has a cascading effect on later quests, one can add another 2 hours of relevant story content throughout the game that is unique to that choice.
Haven is its own entity because there is significant dialogue and story that include main plot discussions regarding the Temple intro, the Hinterlands, companion recruitments, Mage/Templar questline discussions, etc.. There is no equivalent in DAO really since there is no "leadership" to speak of.
I'm combining Haven battle with Skyhold Intro. This serves as a similar "role" to Ostagar (the game's twist). The difference is that the Haven Battle and Skyhold intro are almost all story-related, while the Ostagar questline is inflated with Korcari Wilds exploration (it can be finished in 5mins if one beelines) as well as fights in Ishal. Meanwhile, the entire Haven Battle is scripted (from catapults to Dorian/Cole to Chantry to Last Ditch to Corypheus encounter to "snow sequence" to Skyhold intro).
Arbor Wilds + Well consequence take the exact same spot as Landsmeet + Redcliffe pre-endgame
etc..etc..etc..
Just add up a tally of the typical time needed to complete the main quests while ignoring side quests in both games, and you'll see that they're more or less even. I won't bother to do this, as each player can take a different amount of time doing them, but you can clearly see that there is little to no actual discrepancy.
This comparison isn't even fair from the start anyway as:
1) We're ignoring DLC (which would give Origin the feel of being longer until DAI's is released in full).
2) DAO also technically "includes" DAA, an entire EXPANSION to the game...which is independent of DAO while still potentially having your Warden.
3) DAI also has War Table story missions (passive yet they are still part of the game's story).
4) DAI has more followers with relatively longer and more significant quest chains.
5) DAI has an entirely different mechanic in that there is also the Inquisition to deal with, so there are quests that technically speaking would be part of the main plot but are ignored. This includes zone quests such as Crestwood as well as judgments.