I would guess that the majority of Fiesta ST owner's, on the forum, seats are in fair to good condition, just based on how (relatively) new the car is still, along with the enthusiasm and appreciation most of us have for the car. For owners that have very abused seats, I'd imagine a lot of them are not too inclined to make it look new again. I am not calling you out, as you are a newer owner like me. More so, I am referencing people that bought the car, as it was cheap and fun, then trashed it, which I have unfortunately seen lots of when I was searching to buy one. It could also simply just be that the owner entered the car in a poor way every time, which caused damage to the seat.
If I were you, I would try contacting a reputable automotive upholstery shop and see what they recommend. I've done a little bit of upholstery on other cars, and I've got it to work, but it has never been perfect. Personally, I've decided that anything to do with the seats that affects comfort, is something I would rather outsource. I spend too much time in the seat of my cars to deal with something that is uncomfortable, or not doing its job on the race track or back roads.