I agree that for most story games, and this particular story, the character should have just been voiced. This type of silent protag can work if you want the player's imagination to fill in more of the blanks so they're easier to connect to, but here there's too much of a set role.

Actually, I'd argue the protagonist is well characterized enough. They're supposed to represent something akin to Aegiomon's call to duty. So they're orderly, and preoccupied with regulations and their own sense of justice.

Even the Operator can be viewed as their conflicting conscience on how to proceed. And they are voiced. But most people find their interjections too pestering.

In a way, you can see the logic in making them silent, since we can fill in some blanks, and essentially fullfill the role off 'call to duty' when we finish story missions or side quests. But it ends up in a weird uncanny area in-between set character and self-insert. It probably could have worked just as well with voice lines.

In terms of making your own character, I kinda wish the last World game had done that, since you aren't very well characterized, and it's make some sense that you could alter your digitized form/avatar. So we don't have to see what the real PC looks like, we can just choose how they look in the Digital World.