> which is not the same thing as “in 10 years they will catch up."

This is reasonable, unless SpaceX is stagnating for a decade there will still be some gap in 10 years too.

> The gap is getting larger year by year, not smaller

This is where the reasoning fails me. Unless you're making an unstated assumption about SpaceX or the competitors, why would the gap grow? As soon as there's a decent competitor, SpaceX's margins will get slashed. Their advancement will have to be supported by margins that can only shrink.

Followers can even have an easier time catching up because they have a working model in front of them. The leader has not only to execute but constantly innovate just to maintain a constant lead. The challengers "just" have to execute well because they can copy the leader's innovation until they catch up. And some of the competitors are more than willing and capable of extreme measures to copy.

Is there any field where over several decades the gap between the leader and the challengers just grew? It's not my industry but I have the personal impression that your "gap growing forever" opinion will age like milk left in the sun. We'll see.

Because year by year the gap is growing. I’m talking about a historical trend, and that’s just a fact about it. The gap has been growing, not shrinking.