I don't konw that it was a real breakthrough. It'll most likely become one, but realistically, it doesn't have to be. Robbie has always been a joke hero, and he knows it. Maybe now that he's being taken seriously as a legitimate powerhouse, he' shaving the need to show off. Remember that he is an extremely unstable teenager in a world of adults. In the case of the T-Bolts, mostly unstable adults. Now that he can go toe-to-toe with the heavyweights, maybe he's having the need to display his power, kinda like a lion's roar or a gorilla beating his chest. It could be that Samson was starting to piss him off, so he was showing him what he could really do as a way of saying "back off". Or maybe he can't work through his emotions and just needs to break stuff. There are lots of explanations for the display. I really hope it WASN'T a breakthrough.

I like how Ellis seems to be intimating that Samson, perhaps the most stable and even-keeled of all the superheroes (with the death of Steve Rogers) has his own personal demons to deal with.

And as someone else mentioned, breakthroughs usually do not happen so quickly, so is it that he is useless, or that he hasn't had a breakthrough yet?

Then again, I certainly would prefer it TO be real, and I think it would be confusing if it was NOT real (from a storytelling perspective), but I think it's definitely a possibility that it was not real.

After all, curiousity is, supposedly, what killed the cat!