I didnt mention having alts for storage for a specific reason, but if we want to do go this route... A sub for wow is $15, a single character sub on FFXIV is 13. If you do the $15 one, you get 8 per world. This ends up distorting the whole inventory argument because now its about managing alts and the like. You got to mail things to your alts in WoW for them to have access. Now while you can do this directly, if youre gonna talk about using alts and the like for extra inventory, then all you need is a friend to hold stuff as the go between instead of a mailbox. Little bit more effort, but doesnt stop you from abusing a full account.
Of course an easier method than this, if you got the gil and been at this a while, is to own an FC and transfer items via the FC vault. Though I do wonder if you were to purchase additional retainers, does that retainer limit increase across all alts?
Speaking of WoW, yes this was a common thing everyone did because rather than crafting high end bags, it was easier to create a bank alt and just mail them everything. Which tends to lead me to think that WoW itself has issues with inventory size. But as I said, this has been an MMO thing since the beginning.
I came from WoW initially, and leveled a few alts on both horde and alliance side. So Im familiar with WoWs leveling models.
Now, unless theyve made changes, Heirloom gear is not free. In fact, it was quite expensive to get. Of course Gold buying, inflation, and other factors may have made this obsolete, but then youre looking at buying power with money. But I digress. Conversely, I can get mostly ilvl 120 gear with 2000 poetics at lvl 50, which is easy to get if you have that level 80. That gear will currently last you to 60, where you can replace it with 270. Now if I plan on leveling every class at the very same time, yeah Heirloom works out better, but that method of leveling is fairly unorthodox.
The crux of your point though is that compared to FFXIV which has an MSQ that you have to pass through once on the first play through, WoW doesnt, so it is 'easier'. In that regards, yeah, youre right. You dont have to read a single quest in WoW. You can smash that quest accept, kill boars, and go collect rewards til your an appropriate level, then sit in SW or Org, and just queue for dungeons and never have to see anything else in the game til your up to current xpac. Now for your first play through, Im not 100% sure why you would do this, and most people I remember who get into WoW actually read the quests and play the world content. If you want to argue Choice Vs Design, then maybe FFXIV isnt for you as the FF series has always revolved around a strong linear central story, where WoW it is irrelevant if you exist or not. You arent the hero in WoW, just a hero. You can skip Northrend completely and go to MoP and everything plays out the same. I wouldnt call this method of interacting with the game as a positive personally. When I play an MMO, I want a good story, and the advantage or disadvantage wow suffers from is you can easily out level the content you are interested in. You can sit there and read it and get no exp, or skip past it. But this point is more a thing of personal tastes. Point though is the MSQ itself has its trouble spot which is being addressed as we speak. So beyond that, the MSQ isnt treated as a detriment to most players (with exception to 2.1-2.55) on their first play through. It is a feature. It may have flaws, but this is a personal choice of what you want to sacrifice for it.
When it comes to levling your primary first time through, FFXIVs msq is more efficient. Itll take you everywhere, give you story, and level you appropriately. WoW youre left to kind of pick and choose, over level, and stories get left behind unless you want to complete that quest chain even if it doesnt give you exp. Two different approaches to the initial experience. For Alts, Unless you have stashed cash for Heirloom, you gotta grind and deal with equipment problems which are more difficult to overcome in WoW. If you got that heirloom, strap it on, lvl to necessary dungeon level, sit in org, have queues. Its not much different than PotD in that regards, but at least things like PotD was semi designed for the purpose of leveling alts.