I didn't say the Traix won't be a good sub. I think it would be very good, it just wouldn't be my first choice at its price point.
As for the weight, Funk uses Baltic Birch, which is substantially lighter yet stronger than MDF. It also only has one driver which is using a neodymium motor, again lighter yet much stronger. It won't be a light sub, but it will certainly weigh less than the JTR S2 and Triax.
Also, no single sub has serious output down to the single digits- serious output being defined as that which you could perceive. It's better to have strong output down to where it counts. Here the Funk may have a hefty advantage thanks to its passive radiators, whereby it exchanges imperceptible single digit output for more output in appreciable, yet still very deep frequency ranges.
Also, calling 127 dB over 124 dB a serious advantage is pretty silly. First of all, hardly anyone would want to run either of these anywhere near that loud. Secondly, those SPL measurements were likely taken at an upper bass frequency, especially in the case of the Triax. The 18.3 will have more even frequency response and possibly more output down low. However, if you just want a SPL drag race, yes, I agree, the Traix would probably get louder overall, but there is more to bass performance than raw output. Sound quality wise, one great driver will always be better than any quantity of merely good drivers. Since either sub will give you more output than you will need, it would be better to go with that which sounds better. This is also why I would go with the Sub 2 over the Triax as well, I think its drivers may be qualitatively better. However, one thing about the Sub 2 I do not like is all the different points of possible failure. Six drivers means six times the likelyhood of a driver failure. I also don't like how much energy has to be pumped into it to achieve the same SPL as subs with larger cones, it is bound to get hot in that cabinet, especially with an absurd 240 Volt line, which increases it chances of mechanical failure. The Traix has these problems too, although not nearly as severe. A single, efficient, high quality driver with passive radiators or ports avoids these problem at the cost of some SPL but with the reward of potentially better sound quality.