It feels like a guide because it addresses problems and gives advice on how to fix them. It's not a guide because the advice is just that, advice. Might I suggest not using headers and chapter titles to further remove the illusion that this might be a guide?

I don't really have a problem with what you wrote, I honestly feel it could help a lot of people who struggle with this topic. Though it does differ from my views. That's to say it was a good way to approach the topic, but isn't necessarily the only way to do so.

I have always regarded character sheets as a sort of diploma. It's not a part of the character, and is more to show your qualifications to the GM, and maybe make it easier for people to remember what your character looks like or who exactly they are in the story. 

My definition of progression and development is the same as yours, but how I execute them is different. (I think?) 

Developing a character is actually really simple and is practically automatic to a good writer and roll player. You're just revealing and reaffirming nice and not so nice details about your character, without getting them mixed up. Sometimes you might throw an odd detail in there, like how the mean nasty teacher always spoils her depressed students. This may seem out of character, but the writer or rollplayer who made the mean nasty teacher knows the teacher's secret, and will reveal it very soon. She was mean and nasty to a teenage boy who committed suicide because of her actions. Now the mean nasty teacher isn't mean and nasty to emo kids. While I enjoy twists like that, I don't think good development is just stringing together these types of twists.

Progression, unlike development, is a lot different for roll players and writers. The writer has control of everything, and the roll player has to share the world with the other players/GM. So your optios are often dependent on them, and you don't always get to choose how things go with your character. That's why the best characters (and by extension, the people who control them) are FLEXIBLE! Jill has a thing for Tiffany, which has been lightly hinted at for a while. (They are controlled by different players) So Jill takes Tiffany aside and confesses her feelings. This can go a few different ways. Here are just a few examples:

Tiffany gets distracted, and Jill loses her nerve (nothing changes)

Tiffany's heart is melted by Jill's confession, and they become an item.

Tiffany, mildly amused, tells Jill that her heart already belongs to Amber. Jill now hates Amber, possibly enough to "bump her off."

Tiffany is startled, and reveals she's not only straight, but in a relationship with Bob. Jill is depressed.

As you can see, Jill really puts herself at the mercy of whatever Tiffany says. Of course, a little communication via PM can insure the desired outcome is achieved. Jill's player could ask ahead of time how Tiffany would react to see what they were getting themselves into. they could even plan on something entirely different happening. But the fact still remains that Jill is not holding all of the cards in this situation. That's what makes this collaborative writing. 

While I think progression and development are good things to keep in the back of your head, I don't think you need to spend a lot of time focusing on it. One of my most beloved characters (some even say "best" character) was a British-speaking feline in an alternate 1940's america that opened up a movie theater. He ran away from his home from a fictional island just off of Ireland. The only big reveal was why he left his home, and the only progression was that he eventually became brave enough to go back. What made the character so endearing to everyone was how likable and relatable I made a talking feline. That's not the only way to do it, but clearly you don't need progression and development to be at the forefront of every post.