The lack of the gat/mortar or hades/flak bifecta makes it rather hard to kill something quickly for a Squid, especially since the pilot needs to turn and have a second engineer ready on the side gun immediately, who might be buffing or helping repair/rebuild other stuff.
It doesn't help either that the squid has almost non-existent armor and thus needs to be perfect in term of sneaking up on the enemy to get a minimum amount of damage while killing the enemy.
An alternitive, and more often than not a safer route to quick killing, is to disable the enemy repeatedly until the enemy dies. Carronade and flamer are without a doubt the most reliable close range disable guns.
A decently played mine Squid would probably be more effective in close range since with the quick speed the mines could be everywhere, but mines are usually not as reliable.
A longish range Squid usually loses to most prolonged battles in long range, I believe, especially if the Squid is against long range disable, but the Squids speed allows the ship to reposition rather quickly. Another problem here is that the only longish range light piercing guns are hades and mercury which both have limited horizontal arcs making it either hard or impossible to get a bifecta with the side gun, so long range killing is rarely seen from a Squid.
The problem is the ship's stats. The Squid is probably the hardest ship to fly since it relies more on the initial position of itself than most other ships do, as well as the position of it's ally.
With that I mean, if the Squids gets looked at then there is a high chance that it's armor is almost dead, which takes the main engineer away from the engines and the balloon, which decreases the Squid mobility, which is the ships strongest asset.
Also, most Squids that are not carro/flamer are a bit slow in support because they lose that instant disable power or have no quick killing potential, which often results in a 2v1 against the Squids ally, while the Squid gets ignored for the duration.
You don't see more than carro/flamer Squids, because this is probably the easiest ship in pug games because:
no coordinated enemy team
no reliable chem spraying on the enemy team
carro/flamer are rather easy to shoot even on a full speed squid
In a competitive-ish field most teams just don't try the effort on the Squid, either because it takes too much practise and they like practising what they are already good at or because they fly, or want to fly, ships that are superior to the Squid for the role they are supposed to execute (Metamidion kills quicker than a Squid, Blenderfish is a more tanky disabler than a Squid and so on).
I hope this helped in terms of answering your question.
