Taking a few comments from Reddit about the ins and outs of the QO:
Mostly correct, although qualifying offers are more than a simple formality. The QO is what a team must present a player in order to hold their RFA rights. If a soon-to-be RFA is not qualified, then they become a UFA. If qualified, the soon-to-be RFA can either accept the qualifying offer (and sign a 1 year contract for those terms) or they can continue negotiating with the team to reach any contract. Players are also free to sign any type of extension before the qualifying offer is due.
It's more than just a formality as it creates a very real "floor" for a 1 year contract on the next offer. This gives the player the leverage to reject any poo offer from the team by simply saying "why would I sign that poo when I could just sign my QO instead?" But it still allows the team and player to agree to a multi-year deal for an AAV less than the 1 year QO amount.
QO offer is nul and void if player accepts a contract before the QO deadline, yes. You are correct it would become a formality.
What's not a formality is if the player gets injured or plays poorly and the offer is no longer on the table than the player can default to the QO and get 6.5 million for another year OR becomes an UFA. This high $ QO gives the player a lot more bargaining power than a regular RFA with arbitration rights. So not really a formality.
So it sounds like the Hurricanes CAN offer a different contract if KK will accept it? I guess it depends on when the QO offer deadline is?