First of all, I even said in my post that you don’t need to come close to a 1RM to reap the actual benefits of a strength phase. Doing a 1RM split squat would be dumb, which is exactly why I said not to.
Second, I’m starting to like the idea of tempo runs more and more, but I still don’t believe they’re necessary. As long as low intensity work is in place, it should be fine.
And as for your two points, I just went over one of them in my last post. Maximal strength expression is not limited by training on one leg. The muscles of the working leg are actually under more tension than they would be in a back squat. Similarly, you never even need to approach doing a 1RM to increase maximal strength, nor is there any other reason for lifting that heavy. A lot of sprint programs use reps of 6-15 and still increase their max strength just fine. Hell, lkh can bench press over 400 lbs and he uses sets of 15.
As for your second point, the spinal erectors are not a limiting factor in sprint speed. Sprinting is performed on one leg as well, meaning the limiting factor is the strength of the legs and hips, not the back. Yes, back and ab strength up to a certain point is needed, but the legs need to be relatively stronger than the back during a sprint.