If she left DSN fully loaded, she wasn't designed for combat as she only had a few dozen torpedeo's.
didn't have more than that in the final big push against the Dominion in "What We Leave Behind", either! That is, we don't know how many had been expended in the fighting so far when Worf commented on them being down to 45 torps. The way he says it does suggest they had originally packed hundreds, if 45 warrants the expression "down to"... In contrast, the E-D packed 250 torpedoes in "Conundrum", possibly a "peacetime" load but potentially representative of wartime loads as well. Picard having six times more than Janeway would be in harmony with the size relationships of the respect ships...
We also don't know if the Defiant
was intended to fight with torpedoes or not. She was originally designed to be a Borg-fighter: endurance might not be an important attribute in one-way missions likely to last for all of fifty seconds. She was then adapted for armed recce in the Gamma Quadrant, but only used her pulse phasers in that role in "The Search". Quantum torpedoes were finally used to wound, not kill, in "Defiant", and otherwise remained a secondary weapon in most of the remaining episodes.
In contrast, the Intrepid
often and readily fights with torpedoes even when phasers are an option, both in "velvet gloves" operations (such as the warning shots in "Alliances") and in pitched battles against powerful enemies. She appears less "special" in this respect than the Defiant
, then. Although lamentably, we never truly learn the Starfleet doctrine of torpedo vs. phaser use in TOS, TNG or VOY - apart from it supposedly being a bad idea to use torps at point blank ranges, except that they are used in that very fashion in most of the movies!
As for her speed she only marginally faster than the likes of the Nebula Class which could achieve Warp 9.8
For all we know, warp 9.975 is a thousand times faster than warp 9.8...
As for Science the Nova Class seems to be the Science vessel of the 24th Century.
We only ever saw one in that role - whereas the skies were full of Oberth
class vessels in science and supply roles, sometimes also participating in fights (although admittedly only in desperation fights against the Borg, in "Emissary" and ST:FC).
is the new Oberth
. Perhaps something else is, as we failed to see much of any supposed "post-Oberth