That then, would date the USS Defiant waaay before the other 24th century ships, right? Cause it's weapons are forward-fixed, while other Starfleet ships have strips.
Well, that is an interesting point, because this dwells into the subject of starship design.
Almost all canon and semi-canon Starfleet vessels that I can think of didn't only have phaser banks or phaser arrays and that faced forward, but also to the sides, and depending on the depiction, also facing aft, which we see more of from TMP onwards. Not all ships have both fore and aft torpedo launchers, but many do, though this does depend on their depiction, and Franz Joseph's Constitution is a prime example, with others being the Constellation, Ambassador, and Constitution refit, and the depictions that do show aft torpedo launchers aren't always canon. In non-canon, ships with only forward facing weapons do exist, such as Masao's Torsk, though they are pretty rare, and seem to be more the exception than the rule.
It seems to me that the Defiant class is another exception, rather than the rule, and this probably has to do with the fact that she was an experimental vessel, with the purpose of going in totally new directions if necessary in order to make her as powerful as the design team could manage, though to say that she doesn't have any aft or multi-directional weapons doesn't seem to be the case. True that the Defiant's phaser arrays don't look like typical strips, but she appears to have at least one in the aft of the bridge module, which is seen firing in that other DS9 episode set in the Mirror Universe, and I think that there are also depictions of her having an aft torpedo tube in her schematics or using an aft torpedo, though I would have to check to see if she used an aft torpedo tube in the series. To be fair, I don't remember the Defiant using phaser arrays in the Prime Universe, so I won't discount the possibility that the Terran resistance might have modified their Defiant, though it makes no sense to me for Starfleet not to give their warship defensive weaponry if they can.
As for Romulan ships: From the earliest starship designs, most Romulan vessels seem to only have forward fixed weaponry, until we go into the 24th century, which we then see that Romulan vessels seem to have more weaponry in different locations. Granted, I will admit that I am primely referring to Masao's designs, though I think by now that we have accepted them enough to be worthy of being granted some sort of canonicity, or at least be worth mentioning as an example. The bird of prey shown in ENT appears to have a similar weapons arrangement.
The same thing happens with the TOS-era bird of prey, albeit that in addition to her plasma cannon, she also has ten missile launchers in her wings.
Fast forward to the D'deridex class, and we have a ship with multiple disruptor banks, though granted that these aren't shown firing in any of the series (to my knowledge), so some might see this as non-canon.
It is hard to tell what weaponry complement that the Norexan has, due to there not being any (to my knowledge) closeups of the model using in Nemesis that show all of her weapons, so all that I know that she has for sure is at least a pair of pulse disruptors (or possibly more, I don't remember how many she was depicted firing is Nemesis). There are fan-created 3D models that depict the Norexan with multiple armaments, giving us an idea of what her weapons complement might be, though I know this might not be good enough for some, since there is a difference between canon and fanon. However, if we go with non-canon examples, including other classes, the message appears to be that later Romulan vessels have more than one weapons tube or emitter.
