I think you are ignoring a few things in coming to the conclusion this is "simple".. First, you have to assume Goldschmidt is available, and available at a price that is not absurd.
Then, you have to assume he produces to career norms. I bet Angels fans assumed Albert Pujlos was a safe bet. I am sure the Rays expected far more out of Nelson Cruz. Donaldson did not work out so good and thankfully we got out of the last two years. The last year of most of these deals is far below the player's norm. The fact is that the last 5 weeks Goldschmidt has produced below average. Kepler’s wRC+ is actually 10 percent higher. He is 35 years old. It is quite possible perhaps even likely that he will not produce to his career norms.
We also can't assume ownership will approve another $10M. They are already at record spending. Many teams are going to be restricted on the cost of additions. This isan assumption we can make.
What about the $26M next year? If he declines to league average at age 36 that money could be spent much wiser elsewhere. It could be used for a longer term solution. I would much rather go after an impact bat free agent under 30. OF or 1B being the best targets.
It really simplifies it if you ignore the cost in prospects. Lots of people said the Mahle decision was simple. How much better off would be with Steer for another 5 years and CES has the potential to be dominant bat this lineup is missing for the next 6 years. He would be on the ML roster right now had we played the long game instead of trading for Mahle. If CES hits (even as a DH) to his potential, the Mahle deal is a disaster and here are pondering a similar scenario, granted a pitcher vs a hitter but a 35 y/o hitter.
All of these things are valid considerations. So, I would not be inclined to say it’s a simple straight forward no brainer.