I don't have specific links to this but it's more general reading of tech / military history over the years. I'd love to see a definitive study of the tech tree behind steam engines, but I do know that making bullets/shells precisely fit gun barrels took a long time, and this is analogous to making pistons in engines that don't lose pressure. The first mine-pumping steam engines were the size of small houses and stupidly inefficient, but, assuming lots of coal, they were still cheaper than having people / animals working water pumps all day. And they provided a good opportunity for engineers to properly iterate the technology with commercial pressure. They had a lot to learn though trial and error about how to optimise the things, e.g. adding condensing chambers that separated out initial water heating from power generation. This was all way beyond what the Romans could have achieved.

As you say, with retrospect we can see the Aeolipile as a tech demo, but at the time it was an interesting novelty with zero practical application.