Re: Smaller ships' architecture
"...while the big ships (the "Starships") are deployed for major diplomatic, exploratory and military missions, maybe?"
Not maybe, you essentially quoted the
book (Making of Star Trek,
part II, chapter 3), the way you described it is the way the series' producers envisioned it.
"The first duty of every Starfleet officer is to the truth" Jean-Luc Picard
"We can't solve problems by using the same kind of thinking we used when we created them." Albert Einstein