And you can say well Australia did it, they haven't had a mass shooting since, well they also don't have trucks driving through crowds in Australia.
As you say, the banning and confiscation of guns in Australia and the UK was effective and there has been no mass shootings since the mid 90's. No one is saying guns are the only way to kill people. It does seem to be the most effective way and it goes hand in hand with a big gun culture in the USA that makes guns seem sexy and acceptable.
In places where access to guns are limited, people have used trucks as deadly weapons and home made explosives too. These are also pretty effective ways to kill. It is true that if people want to kill badly enough they will find a way. But.... hypothetically, if US government were to ban and confiscate all guns - however unlikely that would be - do you really think that people would start killing people with trucks and explosives in the same numbers that they do now with guns? Somehow I doubt it.
Its never going to happen though. There are probably dozens of similar threads on this board about gun massacres that have happened over the years in the USA and this is just one more where the same questions get asked - and then it will be forgotten in a few weeks.