I don't agree that it's more plausible that he decided against a better scenario for himself (this is under the assumption that signing the qualifying offer and hitting the market next year would be more financially enriching) because Leonard, Crabbe and Turner made the Blazers such an enticing team that he wanted to "sign for relative peanuts" to be a part of it. I think that's extremely unlikely. To play with Curry, Durant, Green and Thompson? Yeah, maybe a guy takes less. Not to play with Crabbe, Leonard and Turner.
I think after seeing his market was weak, he preferred to take the security of the Blazers' offer over potentially getting hurt or having a poor year and seeing his market dry up completely. I personally don't think signing Crabbe, Leonard and Turner to extremely overpriced deals made Harkless decide to sign.