MGS2 was always going to be about Raiden. There's not only a lot of subtext, but a lot of meta narrative to it as well. It was supposed to be Kojima's last MGS game. Snake was passing the torch to Raiden, as Kojima was passing the torch to his team. The entire way the game is set up with the Tanker visually representing everything people expected from a traditional sequel featuring Snake, and then the Plant being completely different on a surface level but literally going through a checklist of the events of the previous game using it as blueprint for the successor which is also woven into the story. The message that anyone can do what Snake/Kojima did with the right training and under the right circumstances, including how the player is Snake regardless because you, much like Raiden who is also your new avatar, beat Shadow Moses in VR (just like you did). I'm just scratching the surface here, but you get the point.
Kojima kept everything about Raiden hidden from the public. He wasn't shown in any trailer or demo. Kojima also specifically instructed the gaming media to not mention him, and they obliged. He's not on the box art either. It'd be hard to pull off something like this today.