Heh...
I suppose you meant the biggest baddest FEDERATION ship in there? That's also factually untrue; EVERY Federation starship we saw was exactly the same size and same level of "badness" because there was only ever one type of starship they could even afford to show.
There are NO canon references that describe the Constitution class -- or the Enterprise for that matter -- as the largest, or near the largest, or even notably large for the 23rd century. NONE WHATSOEVER. Nor are there any references to its firepower or technology relative to any other Starfleet vessel.
Unless you're trying to say that the Constitution class was the ONLY starship the Federation had at the time, in which case, yes, it is the "largest" ship just because they never built anything smaller.