I'm sorry but did you even read my suggestion or just skim it? This really wouldn't defeat the purpose of personal housing.
1.) Personal houses can be fully customized. Even if customization was allowed on a farm (Again this is just optional.) it would be severely limited.
2.) Personal housing offers much more in the way of gardening. My suggestion was four-to-six spots, think of it as one small gardening plot whereas a personal home can offer maybe three to four times the space depending on the plot size.
3.) Personal housing is being designed as open-world. A farm is instanced, you cannot look to your left and see someone else working on their farm. You cannot stroll down a street and see how your neighbor's garden is doing at a glance.
And lastly if personal housing wasn't so difficult to get due to lack of land which by the way will still be in place even with doubled wards next patch, then this suggestion probably wouldn't even exist. I have a FC with a house, and my own personal chambers I'm really happy with. We've got a stable as well so I've dyed my chocobo a color I'm happy with too. Although I cannot garden given time I can talk with my FC leaders about getting maybe a single spot to plant something and grow it. What I'm doing is suggesting an alternative, a solution for those who are not as fortunate. Personal housing should and always will be the primary focus being it offers so much more. A little farm will at least make functions people want to enjoy but can't because it's gated (Yes gated, land scarcity makes it a game of who can buy up land first when more is released along with the high prices.) available to them. It is still a form of a gil sink too since there is a rental fee whereas once you buy a plot of land it's yours permanently.
This thought came to mind because I'm leveling Botanist, I come across so many kinds of seeds and most are just fodder to be thrown away. They might grow something that could be of use to someone, or just for the sake of enjoying gardens could be planted. But limited gardening spaces and land to grow them on makes that nigh impossible. I honestly don't understand why so many are against something like this, what is there to gain by making gardening and stabling locked behind the requirement you have a home?
Here's something else to consider: If farms existed then it would also leave more space for those who truly want a home and want more than just a place to garden or stow their bird. Some people want to customize a house. Some just want a place to grow stuff and if their FC doesn't offer it a place to store their bird to take advantage of features it offers. They don't want or care about having a personal house because they really just want to enjoy the features that come with it. However they cannot, so they need to buy the land, build a house, and there goes a plot where space is already limited. Giving a farm or plot of land that you can use whenever you feel like opens up more plots in already crowded wards and thus less competition.