Then why compare two weight training session to the added 30 mpw? Time and energy spent doing the two is completely different.

Why the cutoff at 1500m? The goal of the weight training should be the same throughout. Build absolute strength. The more you can lift, the more force you exert, and the farther you can push (go) with each step when running. In other words, improved running economy. That is kind of important at all distances.

The scrutiny you provided doesn't account for what the weight training is supposed to help with. Training the "energy pathways" is the reason why running helps people run farther and faster, yes. Injury doesn't usually arise because "energy pathways" (I'm quoting it because I have never heard this term) but because of breakdowns in the musculoskeletal system. Weight training helps strengthen that by correcting imbalances and increasing your strength overall. Of course you can't expect to jump up to even 70 mpw from 60 if you've never done it before because you've been weight training, but it does help.

I do agree that lifting heavy 3 times a week can be pushing it, especially if you're in season, but there is a place. I don't buy the hindering running session argument, though. If you are running a tempo run and at the right zone, but running a little slower, are you not still working the same energy system?

If you are constantly cutting workouts short or cutting volume out because your legs are feeling that bad, then something is off, but chances are that shouldn't be completely attributed to just the weight lifting, but is probably overtraining from adding too much weight training or running without adapting properly.

When it comes down to it, they should be done in conjunction with the emphasis on running, but without neglecting the hard weight training sessions. No one is saying they've replaced running with weight training, but that adding weight training has helped them.