I know this is a lot of tea leaf reading but if he truly isn't willing to negotiate during this spring training that is a bad sign. If the Angels approach him with a deal around the $400m mark and he refuses it by saying "I dont want to negotiate yet" then I think he is giving you an answer and saying he doesn't want to be here long term. His trade value now is much higher with two years of control left than it will be next offseason and I think you have to explore the idea of trading him sooner rather than later. His market isn't going to improve or decline in the next year, Harper and Machado are his only two "peers" and they've set the market, so there's no reason for him not to sign an extension now if both parties have mutual interest. If his goal is to make it to free agency and go to the highest bidder then the Angels probably won't win that battle anyway and all you'll get is a compensation pick.
The Angels are in a unique position and it would be organizational malpractice not to get as much trade value as you can out of a generational player that you have control of for two more years. Especially if your probable best case scenario is a second wild spot with that player on the roster.