I think it might be useful to keep some perspective in mind in relation to the Excalibur for deciding what is heavily armed. Specifically the Excalibur is already quite heavily armed, so anything at a similar weapons tonnage ratio to it would presumably also be heavily armed for its size.
Our current design if it took just the normal two nacelle is heading for 260.000 tons, this is about 45% more tonnage then the Excalibur, in any case well below 50%. One could take a four nacelle design of course, how ever that's mostly tonnage and space that's already spent on more warp systems then, it does not actually really contribute much to combat capability beyond giving a bit more phaser and shield power, you certainly won't get much space from it.
So I think it's reasonable as such to focus on the 260.000 ton variant for comparison here, as that is how much effective extra space you will be getting. As such, one is getting less then 50% extra useful mass and volume to put weapons in.
Now going by the official spec sheet for the Excalibur it has 1 RPL and 2 normal tubes, so a burst damage of 5 torpedoes, it also has 4 phasers total. So based on this you'd already be getting more then 50% increase of weapons per tonnage if you had a burst fire of 8 torpedoes and 6 phasers.
As such even 2 RPL forward and 1 RPL rear is an enormous 80% firepower increase far beyond the tonnage equivalence, the main difference being that the firepower has become a bit more equally spread out, with the rear being more covered. Even so, this is quite the escalation in firepower and pushing the design a bit more towards being a warship first. Most suggestions also seem to be suggesting more then 6 phasers for the design, instead potentially thinking of 8 or possibly even more, which would be then at least a 100% increase in installed phaser power.
If one really put that much weaponry on this barely larger then a Kea class spacecraft, you'd effectively be heavily upgunning it compared to the Excalibur standard, with it substantially exceeding the weapon density that the Excalibur has. This might not make it a pure warship, but certainly it would be a substantial step in that direction. As such, I think that is something to keep in mind.
To put it another way, In the end unlike the dreadnought and super dreadnought era ships, we did not create much larger ships to hold a vastly larger array of weapons and instead crammed it all in basically similarly large hulls as last gen. The increased engine power basically all going to improve maneuverability instead making last generations ships of more average agility levels, highly agile instead. In that sense I guess what we've done is more equivalent with the treaty era battleships, where one tried to use better technology, more efficient packing of weapons and improved armor schemes to try and get more out of the same hull sizes. And maybe that works for one generation or so, but in the end there is but so much one can do in a same size hull before it starts getting a bit overloaded.
Well these are my thoughts on the current weapon discussions, I hope it is a useful perspective to everyone else.