While there are some reasons to expect that these pathways might act in conflict with one another, the reality is that they interact in very, very complex ways, and attempting to over-simplify their effects can lead people to some false assumptions. Rather than focusing on the potential mechanisms, it is far more useful to lean on outcomes that we care about. In the real world, maximizing aerobic capacity and performance definitely can impact muscle growth and strength performance, and vice-versa. However, very few of those who make the claim that cardio should be avoided to prevent muscle loss could be accused of maximizing anything. 

The very high volumes of aerobic exercise required to achieve peak performance in endurance events are extremely metabolically taxing and could very well lead to reduced muscle growth. Rather than focusing on the complexities of how AMPK signaling might interfere with protein synthesis, a more prosaic concern would be the time commitment. As we have said, maximizing any particular training outcome requires a high degree of time and effort; you simply have to get the reps in. Most nine-to-fivers are just not going to have enough hours in the week to do high volume resistance training in addition to hours of road work each time. Fueling can also become an issue, as many individuals will struggle with both time constraints and the appetite for a high protein, high carbohydrate diet with sufficient calories to fuel training performance and promote muscle growth.