It's not really a matter of opinion, though.
I give you this thread, and any other "gunner is useless, please buff" thread as proof. I do not agree with your, nor any other person's opinion to buff x or change y mechanic to somehow make a gunner "better."
I build my ships to use a gunner. I train my gunners to use various ammo types, even on light weapons. This is my opinion.
You are not adressing my point though.
That being that everyone can fire a gun, but only an engineer can really do his job. You would be right if things like putting out fires and buffing components were available to everyone all the time and the engineer just could do it better by bringing the appropriate tool, but the game doesn't work like that.
If I want to put out a fire on a ship I NEED a fire extinguisher, if I want to shoot an enemy ship I DON'T need special ammo and expecially I DON'T need more then one kind, most of the times. While in every fight you can be assured that you are going to need a tool for rebuilding, one for repairing and something to put out fires because otherwise you are boned if you lack even one of these tools.
That is the problem.
What I'm saying is that there is no incentive in bringing a gunner along, it's just something you might want to do SOMETIMES, but most of the times there is no real reason if you are going for optimization.
As for threads like this popping up it doesn't mean that the issue isn't clear or that the situation is fine as it is. In fact it shows the opposite. If an issue is not dealt with then threads about it will keep on coming.
I'm not saying that gunners are useless, but I am saying that it's objectively the least useful class because of how the game is designed.
The flaw in the idea that to make a class viable you just need to give it more tools for their role is evident in the fact that on some ships even a PILOT is not all that useful. On a Galleon you're better off using ANOTHER engineer, arguably the same is true for the Spire.
Meanwhile no one EVER is going to say "no" to another engineer on board.