Could playing as different Pathfinders have worked?

Wilhelm, please. In Dragon Age, characters barely acknowledged what race you were outside of specific scenes that were few and far apart. Seeing how Mass Effect takes place in a considerably more enlightened setting, the player's race is not going to be enough of an issue that it's brought up in every single dialogue in the game. Yeah, if you're playing a salarian you might bump into a krogan with little lost love for salarians, but that's not going to start a 10 hour long questline in which you try and come to terms with salarian history and the conflict with the krogan. At best it might result in a sour quip from the krogan before the game flips back to the generic NPC dialogue.

Playing a different race should not be vastly different than playing as another gender, content-wise. It's mainly a cosmetic choice, unless it also includes race-specific combat/character skills (such as in ME3MP) and/or race-specific romances (as in DA:I). If they include race-specific story content, it should be something minor and non-critical to the main plot, unless it can be implemented with minimal effort.

The more fixed the protagonist is in the backstory of the game, the less flexible roleplaying opportunities become. With Ryder, you rarely if ever played YOUR character, you played an almost entirely predefined character with a predefined past and a predefined family. If you liked that predefined character, good for you. If you didn't - as was the case for me with Ryder - then you're shit out of luck. This was a problem with Shepard too, but not as big as it was with Ryder since you could choose Shepard's first name and origins/military background.

The fixed protagonist is also one of the few things I really disliked with The Witcher. A pretty interesting world but you're always stuck exploring it in the role of Geralt.

The only reason those prologues worked was because the Warden wasn't voiced.