Considering FFXI has around 500k active accounts on its prime, way before XIV was even released, I'd say your estimation is incredibly generous
What about the Relic/Anima weapon ? You have several stages to grind in order to have one the best weapon of the expansion. But, would it be very different if all those stages were released at the same time, and earlier stages were nerfed during the expansion lifetime like they are now ? Since none of them actually required dedicated content after Chimera and Hydra, there's nothing preventing it.
I don't think Yoshida is taking the "safe" route, he's taking the "short" one.
Let me explain...and recall some painful memories of my time in XI...
Once upon a time, I was a new player. Like all new players, I reached level 10 and made my way up to the dreaded Valkurm Dunes. It took at least 20 minutes to reach the place, probably dying once or twice in the process (Thus losing XP), 20 more (When lucky) to join a full party, for a one-hour grind (before anyone ragequit and the party dissolving completely), with several more deaths...
In the end, I needed 2 hours, to, maybe, lose progress because the XP loss might be higher than the Xp gained. That's the harsh route.
Now, you add Aetheryte teleport, you remove the need to grind in a full party, you remove the death penalty, and suddenly, I could have gained the same Xp in a mere 30 minute session. That's the 'safe route'.
The same is true for dungeons. Wanna do Salvage, Nyzul or Dynamis ? Great ! You have 2 hours in front of you ? No ?! Don't bother...
As long as players can progress by small session, they'll have no issue if it takes time, even when being casuals. After all, in the end, everyone will be at the level cap. And since every instance has an adjusted level, you'll have absolutely no issue finding someone to do content with you (Ok, maybe not for Meridianum and Praetorium...)