I think the fourth line should not be ‟Voice wielding power”, but instead ‟Voice-wielding power”. In Dragonborn lyrics there are words ‟And the voice, he did wield, on that glorious field”. (By the way, are the commas correctly placed? I would write it as ‟And the voice he did wield on that glorious field”.)
Doesn't this line mean ‟the power of wielding Voice (Thu'um)”? There were others capable of using Voice, but it took very long time to master it. For the Dragonborn it's natural and I think it's about the power of wielding Voice, not the Voice which wields power.
There is voice, then there is the Voice (Thu'um). Capitalization cannot be expressed through speech, so let's consider both possibilities. In the case without hyphens, the phrase refers to the dovahkiin's voice, which has power infused into it. In the case with hyphens, the phrse refers to the dovahkiin's power to wield the Voice.
The clue given as to which version is being used comes in the next line, which is "of the ancient Nord art". Taking this line into consideration, when reevaluating the possible phrases it becomes clear which term is being used. In the case without hyphens, the entire line refers to the dovahkiin's voice, which wields the power of an ancient Nord art. In the case without hyphens, the entire line refers to the dovahkiin's power to use the Thu'um... but then there is a grammatical error. Specifically, the word of. There is nothing for it to describe. In the first case, of described the power as being an ancient Nord art. In this case, there is nothing it describes, and so it is an error.
Seeing as how only one interpretation of the term Havelock gave that stands up under scrutiny, it becomes clear that there is in fact no hyphen.