It highly depends on exactly what you're trying to do and must be evaluated on a case by case basis for each tool. Some will be easy. Some will be hard. But overall the ideas skew towards the hard.
The quote taken is an answer to a specific case.
Also we don't know if ammo will solve it. We also don't know if "substantial" changes will solve it. Each solution will bring ups and downs and they all need to be evaluated objectively. We can't go in with any assumption regarding any solution, only a goal and timeline of when the tests can happen.
I've already given more than my fair share of cents in the Ammo discussion, even a couple ideas, I still stand behind my idea for a reloading tool for the gunners (if you want to read into the details go to the ammo discussion pages 3, 4, and 5 have comments form me about it). Its simple does not affect too many mechanics and no touches to the UI so it should not be much harder to implement than any new form of ammo.
I unfortunately cant think of any tools that could work similarly with the gunner just sitting on the and selecting it except maybe increasing the weapons armour and health which could also be achieved from ammo if it were programmed to, or perhaps a weapon that locks the aim in place for a few seconds when activated but reduces all recoil to 0 like heavy clip but can be used with any ammo type.
The game is by no means broken in my opinion, I love the fact that 3 engineers, or 2 engineers and a buffer can be a completely viable build, and i hope the game still allows that in the future. However I would also like to see 1 engineer and 2 gunners being a viable build on sniper ships or something which is not the case currently.
More ammo types seems like a good idea to me, especially if they are highly powerful but specialized, but i would also like to see a tool or two for the gunner to differentiate them more from the engineers when behind the gun. Just having ammo can usually be used by the engineers and ammo types that damage the gun do kinda support engineers more as they can repair faster (as others have already mentioned).