That is suggested specifically to address the shell FCs, since you are correct that it's completely invisible to a healthy FC. However, that's the entire point as it's a deterrent to make it harder for the shell FCs to tie up housing while not affecting the legitimate FCs.
That said, if someone is willing to fork over the money to maintain the account subscriptions needed to pass the FC check, they can keep the house as I'm not distinguishing who is controlling the subs, only stating that they should exist and it should be applied to all FC housing equally. And really, if someone has the disposable income to fund it, who am I to tell them how they should spend their money since it's more money going to FFXIV and we all benefit from that.
Running the math on this, if you have four service accounts, with 8 characters each, they would only be able to tie up 12 houses between the accounts assuming you had 32 characters rolled and ready to go. That's 8 FC houses (as IMO the FC housing restriction that SE has isn't good and it should go), plus the four personal houses from the service account as each FC would need to have a character from each service account to stay compliant, so in essence, each account could only tie up 3 houses. To own a ward, you'd need 12 service accounts (which would be a theoretical maximum of 36 houses which IIRC is slightly larger than the size of a ward allowing for some flex in the houses), and if someone is willing to pay 12*$15 USD = $180/month to keep the ward (or more realistically $150 USD * 12 = $1800/year as 2 six month subs are about $75 USD) then more power to them as they are helping fund FFXIV. However, when you start getting into that much of an annual expense, the financial cost starts to become it's own deterrent and most people would seek to divest the houses at that point... which is why everything listed needs to be present for it to work together correctly.