Protagonizing the PCs, as though this were some cheap novel instead of a believable world.
I don't think I understand this one. I think you mean to relate this back to your second point, "enforcing preferred outcomes", but there has never been a time in the history of D&D where the PCs weren't protagonized, and deprotagonizing the PC's as I understand the term is a terrible sin.
PC's are protagonized when they are given advantages relative to ordinary persons in the world and placed in situations where there are adventurous or even heroic possibilities near at hand which they have the resources to overcome the difficulties inherent there of and are allowed to do so.
This is the normal narrative of D&D and always has been.
Breaking that down into components, 1st level PC's have always been uniquely and unusually capable individuals. They are not ordinary, but rather have potential, abilities, combat skill and even gear far in excess of what a randomly selected individual in the fantasy world is likely to have. It is as if we've rather deliberately selected a non-random individual within the fantasy world who is likely to have an adventurous story. This is protagonizing the PC.
Secondly, those same characters are 'coincidently' placed in a time and place where adventures are at hand. We don't start the story in an ordinary time in a place of peace and plenty where heroic conflicts are non-existent or unlikely. Rather, we begin the story with the non-randomly chosen individuals of heroic potential are near at hand to some sort of place or event which provides for them the opportunity to reveal and unlock their heroic potential. It is as if we've of all the persons of the world whom we might focus on, chosen the ones which are most likely to find themselves involved in an adventurous story. This is again protagonizing the PCs.
Finally, of all the 'interesting times' that a person could be involved in or involve themselves in, we've chosen ones where the PC's have at least some chance of success. There are definitely people, even ones with the PC's advantages as PC's, in the believable fantasy world that find themselves suddenly beset by a rampaging ancient red dragon, or a horde of elite hobgoblin cavalry marauders who have no choices in front of them except to die in a futile manner, but we haven't selected those believable persons to be the one whose story we are telling. We might not prevent the PC's from putting themselves into that situation if they insist on foolishness, but we have certainly chosen characters who are in a situation to succeed if they choose to do so. And that is also protagonizing the PCs.
Technically, you could protagonize PCs even if they were 0th level commoners in a placid setting facing only ordinary non-heroic challenges with their ordinary skills. But not only does D&D not do that by its standard rules, but instead has ideas like hit points and PC classes and roll 4d6 take the best three and starting wealth and so forth, but D&D doesn't traditionally do that even with its established procedures of play. Rarely in D&D's history have we seen suggested procedures of play that don't protagonize the PCs - the only exception to D&D specifically protagonizing the PC's I can think of is the infamous period in the early 1990's where TSR for the Forgotten Realms setting came out with a series of heavily story driven adventures where the PCs were not the protagonists, but only henchmen of the protagonists and largely helpless observers of the great deeds of the adventure's true protagonists - all of which were NPCs - and had no ability to actually effect or choose the outcome of the story. That is what it looks like when you deprotagonize the PCs, and ironically that very much was intended to support the game world as cheap novel, and not the game world as a believable fantasy world.