To begin with, you answered your own question. The goal IS to win now. Buying, or trading for talent is exactly why they would consider trading Mateo.
In the second quoted paragraph you again make a point in my argument which is the need for starting pitching. If you believe the org’s top priority should be acquiring that then how do you propose they go about it if not trading away a surplus of talent? You say Mateo is a “nugget”, well then he’s also a chip. They’re loaded positionally, you said so yourself. If Mateo has figured it out with the bat then he’s valuable. Valuable enough as the lead piece in a trade to get the team the starting pitching they need.