You're not *advocating* that the Rams play hardball. You're merely pointing out that the Rams hold the most effective bargaining chip. 2 more years on Donald's contract, PLUS the franchise tag for another 2 years. Aaron Donald knows that he's worth more than his current pay, but he ALSO knows that the NFL is not for long, and he can destroy his value by 1. refusing to play at all, or 2. insisting on a blockbuster deal that would put him #1 defender in the league (which the Rams won't take), but then getting injured (it can happen to anyone!) during his rookie contract or franchise tag, and also reducing his market value.
I think I'm reading you correctly that you know and I know that Donald doesn't want to take either one of the above risks, and the Rams don't want him to take those risks either. So yeah a deal will get done, but I'm seeing what you're saying: the balance of power is in the hands of the Rams at the moment. The things Donald can do (refuse to play or refuse to negotiate and end up getting tagged) both risk reducing his value.
Donald is a sharp guy. He'll make the right decision.