Stronger? Maybe. I don't know the strength results of either of them, and I'm not really interested, because I judge them based on their appearance/bodybuilding.
But I don't think he's bigger than Mike Mentzer. I mean in terms of lean tissue. If you put them side by side on stage and weighed them, I think Mike Mentzer would be bigger.
I know you like Dr. Mike, but it was Mike Mentzer who—based on Arthur Jones's theories—created principles that are still successfully used today. The same can't be said about Dr. Mike, which is why Mentzer is so respected by millions of exercisers worldwide. In today's hypocritical world of pseudo-experts and celebrities, few people can build trust that will stand the test of time. Besides, the best has already been invented; I don't think science will invent some special, new training system. And even if it does, it will be based on principles from the last century.
A muscle must be forced to do something it has not done before in order to develop, and this can be summed up in any training method.