You keep insisting "reasonable self-defense weaponry" and yet literally
nobody has given me an expected OpFor composition, capability set, and armaments mix to show why this is reasonable. For all I know, your "reasonable self-defense weaponry" might render the ship
underarmed because the actual reasonable OpFor expectation is significantly above what you're doing. Presumably tactical is also made out of intelligent people, who are aware there is this thing called "roles," and a ship designed to operate in
friendly territory
close to friendly bases for
scientific purposes doesn't need significant armament. To say nothing about the fact that tactical would probably hate it even more if their hard-charging naval captains are forced to spend tours of duty scanning space rocks.
And sure, there are no Star Trek ships in Alpha Canon that do not have torpedoes - the same Alpha Canon where the Federation is the dominant peer power in its sector, with significant industrial and technological advantages over everyone else, such that they can build exploration vessels that, despite the tradeoffs made to become multirole explorers, can 1v1 dedicated warships of comparable size or mass.
@BungieONI mentioned the fact that there isn't any reason to believe
current era torpedo launchers are multirole, again because the current era Federation isn't the same as the Picard-era one and may not have invested enough into making those tradeoffs hurt less.
Finally, people keep talking about how we need resources to design and build escorts and that's bad but don't recognize that this sort of resource crunch generally makes specialists more desirable than generalists because you need to marshal resources effectively and that means not wasting industrial capacity on things that exist solely as emotional support.
"Space is dangerous" is
not a valid reason for putting emotional support guns on a survey ship. If "this is Star Trek" was enough justification for design decisions, this quest would be over because the ideal option would to be to crib from a Star Trek technical manual every single time.