Well, exrx.net calls it dangerous, and having had my only weight-related injury from it, I have to agree.
1)Like any exercise it's only dangerous when done wrong. Hell Plant Fitness thinks the stability balls are dangerous! EXRX is just covering for liabilty issues.
The injuries you listed are associated with doing these exercises with poor form(Maybe you didn't but in most cases that's the cause)
I see that you disagree with the Friels. Back in the early 70's I used to do only trad lifting, but when Friel's CTB came out, I switched to doing it their way and had better results. YMMV.
2) Yes Friel's method is just periodization, but he donesn't have you do endurance that early in your program,and I don't recall that high of a rep range either.
I'm curious how you define "anaerobic." A properly done set of 30 takes 1 to 1.5 minutes, about the same length of time as a power interval. That fact that it would be impossible to continue for more than another 2-3 reps, or another 30 seconds in the case of power intervals, had always led me to believe that these intervals are powered by anaerobic reactions.
3)You must be flying through those reps It takes me around 45-60 sec for a set of 10. (see #1)
I'm also curious about your statement that HIIT work "becomes aerobic pretty quick." How is that?
4)Yes take Tabata for example (20sec on10 sec off x5minx1min recovery repeat 4-5 times) Any event/activity longer then 3 min or so relies mostly on Aerobic metabolism for energy. It gets to the point (because of short recovery periods) that you cannot hit the same high intensity for long so the activity relies mostly on the aerobic system.
If you really want to do mostly Anerobic work short work period(2min or less) with a longer rest period (full recovery 2-5min) Then you'll be doing true anerobic work.
Being a road cyclist rather than a track sprinter, I'm also generally curious and somewhat skeptical about heavy squats and deadlifts, vs. using a leg sled or press. Being of an age, I have arthritic facets, lumbar stenosis, thinned discs, and one disc with a compression fracture. Thus I'm somewhat disinclined to load my spine with exceptional weights. Moreover, it seems to me that these spine-loading lifts do not very well replicate the forces of cycling. I know that I pull up on the bars some when sprinting and climbing hard, but nothing like multiples of bodyweight which those lifts produce. Seems to me they go against the principle of specificity.
5) Maybe not for you but spinal loading is very improtant (even more so for cyclists) for bone density.
That said with your back issues you can still do vaiations of Russian Deadlifts no spine loading. Much better then a leg press/sled. My question if you have issues with spinal loading why use the sled? Doesn't that comtribute to spinal loading to some extent? Using machines takes some much away from these exercises
Are you familiar with this meta-study?
http://www.sportsci.org/jour/04/cdp.doc
Perhaps there are better and newer studies? My reading of this one says that trad weights are perhaps the least effective training modality for road cycling.