This is true, but it doesn't mean that gun control laws aren't helpful or could not be helpful in preventing similar situations.
Would anyone at all disagree that the situation would be far worse if the shooter possessed a fully automatic weapon with a large ammunition capacity? But, in the US, we have bans on automatic weapons so thankfully they aren't in wide circulation. If semi-automatic military-grade rifles were illegal to possess in this situation there would have been one more step in this story where he could have been stopped.
Sure, several people have pointed out that there are many other ways to harm people, but few if any of them are as simple and easy as legally purchasing firearms. Producing explosives is still something that he would have to learn how to do, actually do without blowing himself up, and would put him into several situations where he could be arrested. And honestly, I doubt it's nearly as easy to kill and injure people by driving a car into a crowd. People can much more easily scatter and run from a single car.