To me, this is definitely a complicated question that depends a lot on the engineering specifics. If it had stuck to the question in the title, and asked primarily about that in relation to faster bullets, other things equal, I could maybe see the case that it's on topic as conceptual.
I'll address your points as best I can.
A bullet penetrating a plate is absolutely not a "trivial engineering construction". Impact mechanics are fairly complicated, let alone the mechanics of a fast moving object shearing through plates. It's not always trivial; depending on the properties of the materials involved the problem may change quite a bit.
This question focused on a series of particulars, such as changing the material, increasing the speed, and greatly increasing the speed. The particulars are the focus of the question, which makes it quite broad. I may have voted to close it as too broad myself.
In my opinion, due to how many factors the question asked about; this question can give the wrong idea in several different ways, instead of glorifying anything. If people answer it without addressing the broad range of different situations, it may give people the false impression the situation is more simple than it actually is. If people actually try to address everything, it will give the impression that this site allows questions that require entire chapters from engineering books to properly answer.
Coming from experience, this is absolutely the type of thing you would find explained in detail in an engineering textbook; in terms of the details OP seems to be asking about. I can't see any physics textbook digging into all the different conceptual details to answer this. It really doesn't seem on-topic here unless it can be revised to focus on a specific physics concept; instead of the broad application of many.