Invocation of the 25th Amendment and the impeachment route are not mutually exclusive. The vice president and the majority of the principal officers could prevent the president from exercising the powers of his office by activating Section 4, giving Congress time to impeach, convict, and remove the president—and disqualify him from serving in federal office again.
The real benefit of the 25th amendment is its efficiency. The vice president and the principal officers of the executive departments can make their decision free from parliamentary rules and transmit the results to Capitol Hill within minutes—quickly enough (in theory) to stop Trump from trying to derail the proceedings by firing enough principal executive officers that it becomes practically impossible to know who the relevant executive officers are for 25th Amendment purposes, or whether they can exercise authority under the Amendment.
This possibility of Trump attempting to preempt a 25th Amendment action against him highlights that the amendment was intended, as Kalt notes, primarily “to provide continuity of power” when a president is truly disabled. It was not intended as a mechanism to remove from power a physically functioning president who simply lacks the capacity of character to perform his oath and who is wielding the powers and platform of the office in historically destructive ways. This and related concerns are why Kalt counsels hesitation against using the 25th Amendment for all but the most extreme situations that do not involve physical impairment.