It'd still be able to deal some damage to another ship on its way down if someone came along with the intent to just sink it rather than loot it, enough to make such random attacks risky and pointless. Which is.. not the case in Elite, where Rinzler's guide to trading in open literally says to ditch the guns to save weight since you don't stand a chance of getting through the shields, never mind winning, against a dedicated combat ship.
All of my CMDR's trade ships are fully armed and sufficiently armored to be competitive with pirate-class CMDR interdictors flown by peer-level pilots. Blockaders or gankers in pure warships will best my trade vessels in combat (again with similar piloting ability), and they should.
The overall situation is, if anything, more in favor of my trade ships in ED than a war galleon vs. a treasure galleon in the age of sail.
Rinzler's guide is geared toward novice CMDRs who just want their ship to be able to survive an encounter long enough to escape. It does not imply that more active or proactive resistance is always futile where there is more of an experience parity.