The concern over increasing easy running is that i have very small joints and a normal sized body. Obviously if i'm elite level i can only expect a few rotations before i'm superseded by new guys coming in, but as an amateur i ought to consider a bigger, more long-term picture. The threat is that i wear my knees, ankles, and hips out to the point where i'm goosed at about V60. I have plica syndrome in both knees which affects my cycling, but this can be rectified with surgery at some point, a thinned out meniscus or worn out hip is basically game over.
The only realistic long term strategy for a better aerobic base is to cycle more, i have no chance of winning anything so there isn't even any payback for more running and subsequently more joint wear.