So basically Miranda Class is just the economy version of Constitution Class, and not a starship that designated to conduct different missions and different purpose?
^From the way the were used in TNG - it almost seems like the Miranda/Reliant type ships were an easily convertible/adaptable platform that could be converted to serve any number of different purposes...but only one at a time - cargo, science, defense - *mainly* (with probably limited capacity for other tasks - but not as much as a Constitution Class...)
...compared to the Constitution/Enterprise type, which seemed to be able to multi-task better, and serve any number of functions at once (but probably not any one of them quite as good as a dedicated to that one single task ship might have done.)
Then again...the Reliant was a science vessel *and* a formidable warship...so maybe the Reliant/Miranda was just a less complicated, easier to mass-produce mini version of the Constitution/Enterprise...?
(Please excuse me...I've been sick and on meds...my heads a little foggy and it's difficult for me to...communicfiate...afy...whatever...)