Your argument was that the range of actual frigates was very limited, and so we should reduce the range to 1 tile (like late-game archery units), but their weapon was the cannon. Individual cannons on frigates were inaccurate, but their range was much greater than an archer. If you nerfed frigate range based on "realistic range", you'd have the problem of archery units still with "unrealistic range", and you'd also have precedent to limit the range of cannons.
The whole point of having a 2 tile range is so that a ranged unit can support a melee unit, especially during a siege. Nerfing frigate range will make it impossible to capture a well-defended city from the sea until battleships.
first of all, range is not the same thing as actually being able to damage something. Yes, a cannonball was shot for half a mile, easily. BUT at that range, it didn't actually deal any damage anymore. Actual combat range for those cannons was much, much shorter. Arrows that fall down on a formation are a serious threat, even at max range.
as for the gameplay issues
Also, a well defended city should be hard to take! A city that only has 1-2 land tiles next to it is almost impossible to take by land, I agree with that. But that city would still be easily taken by 1 range frigates because of the sheer number you can get in range.
However, a city with only 1 coast tile can be bombarded by up to TWELVES frigates per turn, and even if it's a straight coast line up to SIX frigates can bombard it. That is enough to gun down a city
Your whole argument stands on the premise that a frigate fleet should be able to capture a city with only 1 adjacent coast tile by itself. A premise I doubt many players would agree with. You even contradict it yourself with that statement
"The whole point of having a 2 tile range is so that a ranged unit can support a melee unit, especially during a siege"
What is it now? Should Frigates support a land assault on cities with 1 coast tile, or should Frigates be able to carry out the entire assault by themselves?
What does this mean? That no one in a position to build Frigates is limited by their iron capacity?
This means, by the time Frigates come out, you should be sitting on so much iron it won't be the limiting factor anymore.
Without wishing to offend anyone, I find all the threads on 'this or that unit is OP' a bit odd. It's a strategic game; these are the pieces and these are the rules on what they can and can't do. I personally consider threads on imbalances within/between civs to be a valid premise, but single units? As well argue that some chess units are OP or not true-to-life.
If catapults could shoot 4 tiles with indirect fire and deal the damage cannons deal now, would they be balanced just because everyone can build them? If one unit dominates all other units to the point of the only way to counter a bunch of said unit is also bunching the same unit, there's clearly something wrong.
And just because the AI is too stupid to properly abuse this strategy doesn't make it any less silly. There's people who play multiplayer, and all forms of island multiplayer greatly suffer because the renaissance just becomes frigate spam.