Pinker never said that wars have stopped, just that relatively speaking, we're in an exceptionally peaceful point in human history, and he's far from the only person to do so.
Statistically speaking, he's right, and even then, relative deaths from war have declined. For instance, WWII killed around 70-85 million people, so in total no. it takes the top spot, but in relative terms...well, fun fact, if the Mongol Empire was formed today, you'd be looking at a body count of 800 million if we assume the 'death ratio' remains consistent. Relative numbers give us a better look at progress than absolute numbers.
Whether the "Long Peace" remains long, of course, is another matter. And even then, you (and people have) made the argument that you can draw comparisons to past periods in history where things seemed peaceful, and then war reared its ugly head again.