It's been beaten to death here about f2p vs p2p, but I wouldn't mind hearing your explanation on how p2p screws people.
It's a matter of what's offered by the game and what you participate in. Let's just throw together a list of potential activities:
1) Leveling combat classes.
2) Leveling craft skills/classes.
4) Solo challenges.
5) Small-group Dungeons.
6) Large-group Raids.
7) Achievement hunting.
8) Pet collecting.
9) House construction.
10) Wardrobe management.
You can add more, I'm sure, and say the sub model is a good value, but that depends on how much of the above you actually care for. The question then becomes how much of your $15/mo goes toward the things you enjoy to receive yet more of it. If you're someone who's only into 1, 2, and 3 where you cap all jobs/crafts and finish the story content, what do you do? Do you keep paying in hopes they'll add stuff for you in the next patch or maybe take a break? What if you pay for 6 months and get nothing new? Might you feel a little ripped off?
This is where loyalty can be bad as a consumer and leads to complacency from the developer. No, not everyone is going to like or want the same things out of SE, that much is apparent if you read a few critique and request threads. And I would hope that SE is internally tracking everything players do so they could put out stuff like a census saying, "x% of players have beaten this dungeon!" or "y% of players have leveled Gladiator to 50!' That kind of data will tell them the things players are into and will hopefully influence more of that content development. The exception I anticipate out of this, as seems to be the case with a lot of other MMOs, is #6. It doesn't matter how small the percentage of the population is that's beaten raid content (while boasting everyone else does it), it unfortunately seems the endgame focus and continues to be an avenue of exclusion for many.
But let's say the game is free to log in and take on basic tasks like 1, 2, 7, and 11 with the first dungeon available to let people have a taste. If you find you like 5, you could pay $3-5 for each dungeon after. But you might think, "There's like... 8 dungeons! That'd be $24-40! Rip-off!" How many dungeons would you realistically expect to come out in a 3 month span? Even at the most expensive end, that's less than 3 months sub and you're doing what you want. Stuff like costumes and pets have already proven successful in other games as simple fluff items, and hardly required to play. I'd also say the same of housing. Role-playing isn't something you can fundamentally charge players to do unless it's stuff like new emotes or scripted actions. Again, fluff. Achievements can certainly wiggle their way into all avenues and reward anything from titles to pets to mounts and then some. Realistically, these should also be limited to fluff, but sometimes "must have" items slip through. And if for any reason you want to take a break? There's no guilt about have 15 days left in the month feeling like your money's going down the drain.
While it may be simple to liken it to up-front payment against payment over time, a good F2P should be cheaper in the long-term for many. A sub model could even remain that offers content for free as well as discounts on the fluff things. Of course, I'd also make sure players have the option to "buy" new content with gil or some kind of currency they can acquire within the game itself. Have trial periods, promotion codes, bulk sales on things like dungeons, basically anything to tell consumers, "Hey, were making stuff! Play it!" And if people like it, they'll buy it. If people don't like something in a sub model? Well, they're usually not given much of a choice to explain why. It's either pay for that stuff too or unsub. In the end, even if you're happy, it doesn't mean everyone else is and addressing their grievances can't lead to a better game for everyone. That's why I've always hated the, "If you don't like it, quit!" or "Maybe this game isn't for you!" rhetoric that some like to spew. Like it or not, they've helped pay for a game you enjoy.