Retainers, confirmed, you have to pay for them.

[Yshnal]

Because a character slot is completely different from a retainer. Unless you can play your retainer and go fight Titan with it?

Yeah, and also 8 character slots per server up to 40 in total (plus their inventories, armory, armoires, the two basic retainers, etc.) require more resources than two simple retainers. Not to mention what I stated, there's a difference between a discount and charging more. Keep in mind that the price on the standard sub is, well, the standard pricing for the large majority of P2P games. That's why both subs have the names they have.

And that's why the monthly extra for the two retainers (for each of them) is not seen as the difference between the entry and standard subs, coupled with the fact that even F2P MMOs with no sub charge you just once for extra inventory.