I'm curious what you mean by "soundless inner monologue"? I don't really experience much imagery at all but my inner monologue feels very close to how talking to myself aloud feels, so I wouldn't describe it as soundless. The verbal vividness of my internal monologue is actually how I imagined people with good imagery skills "see".

On the note of advantages, I know I have something weird going on with the back right of my brain specifically (focal slowing on EEG among other things), which I am pretty certain connects to my favoring of verbal over visual thinking. So I guess it depends on the cause of a case of aphantasia, but to me it feels a little like how blind people end up with heightened hearing. I think I've really developed strong verbal skills because of it, and there are definitely advantages to having strong verbal skills.

I recall a professor showing us a study once where students performed better on an exam when they were allowed/encouraged to talk out loud to themselves while they were taking it. He was encouraging us to talk through stuff with ourselves, but at first I found the result weird because I assumed everybody was always talking to themselves in their head. That was the first time it really dawned on me there may be large individual differences in how we experience thoughts.