Making comparisons isn't going to help because things are different in star trek. A frame has no effect on anything relevant to STO, you can check the size of Bugs, defiants, and Nova class vessels for it if you need a modern comparison of what is needed for the process of upgrading.
You're seriously arguing that size has zero impact on a ship's capabilities in Trek?
Why then did Voyager take priority over the Equinox based on tactical capability?
Why didn't Peregrines carry the same amount of firepower that the Defiant did?
Why didn't the Defiant have the equivalent staying power of a Sovereign-class ship?
I could go on and on and on, but the notion that size is irrelevant is complete bunk.
Secondly, you're using modern designs to argue for an obsolete and ancient design. If ships could be upgraded like you argue, why then didn't the Federation just fight the Dominion Wars with nothing but upgraded ancient Connies?