Bennett would actually be worth more to Seattle if he is unqualified (assuming he accepted the qualifying offer). It would give them the opportunity to offer him a more suitable deal (smaller AAV, longer term). If they can't work out a deal, they could always qualify him themselves.
I think that because he makes more than $1 million, he only needs to be qualified at 100% his current base salary.
https://www.capfriendly.com/qualifying-offer-calculator