Basically ISU can sit out of range and be rushed. At the same time, tiger needs to be in range all AT guns and tank destroyers (including ISU) to do anything. Both are doctrine tied.
Vacuum comparisons are really wrong. Byt vacuum comparisons of lategame units are just horrendous. ISU will always be supported sitting relatively safely behind the fronline dishing damage. That is basically its strength.
Actually you're wrong, vet tiger is a machine and can quite easily slip into engagements with its extra range that premium meds and even vet0 is2 lack. All can't fire back due to tigers extra range
Obviously TDs can fire a shot off before tiger gets close, if they couldn't Jackson etc would be useless