I've worked on very high current automotive applications in the past. While you raise some valid points, there are generally solutions to them. I've found its best to think of these things on a unit level - which is why so many battery characteristics are quoted in that way. If you can think of solutions for how to get around these issues for a single battery on a bench, there tend to be tractable ways to scale them.

Heat dissipation is one of the only things that doesn't scale linearly. 6kw sounds like a lot of power, but over 10 minutes, you are only talking about 1kwh of energy - about enough to boil 10 liters of water. Given the mass of the 100kwh battery, a large fraction of that could just be absorbed as temperature gain. If you assume the specific heat of iron (which is an underestimate) and the weight of the current 100kwh batteries, its about a 13 degree C change.