I think this a point that AA guns were too short ranged and typical DD gun mounts too slow to track PT's. I am convinced that best weapon against a PT's were fighter bombers and PT hulls with guns for British: MGB's specially because being numerous, so a good simulation would rise this weapons in typical scenarios.
Best against PT boats were float planes who can fly at night and follow their trail for hours.
Dont get this about AA guns not having range , AA Guns have huge range ,100mm and 127mm guns your looking at 18-20,000+ Yards. The 25mm had a range of 8000 yards and were used on land against tanks. I do accept that many deck mounted AA guns had a MINIMUM range. Torpedo effective range was 1000 yards.
DD Guns could track planes so i don't think a 40 knot PT boat is an issue. Besides when the boat is spending 5 minutes closing the tracking doesn't need to change at all your not going to be doing 20,000yard circle
Lets check this out lets assume a stationary target
Distance covered in a minute 1.2km .
m radius training needed assuming 100% lateral movement
20K 3.4 degrees / minute
10K 7 degrees / minute
5K 13 degrees / minute
2k 34 degrees / minute
1K = fire and go home. ( would be 69 degrees per minute or about 1 degree per second) .
Some guns
5"/40 6-7 degrees/ second
5"/50 ( On most destroyers) a slow 4-6 degrees per second
1" AA gun 16 degrees / second
As you can see with 100% lateral movement guns will still train effectively on a PT at all distances greater than 250 yards.
(Also note against 33 knot active destroyer , your relative speed is like 7 knots.)
There is a good reason they were used at night or in ambush , guns will shred them which is why in US doctrine they used Smoke after the surprise. At land they can hide behind a piece of land ( like the Italians often did) and not be spotted when a ship gets near they can rush the 3-5000 yards in 2-3 minutes with a bit of luck they will not be spotted until half that time is up and hence are only exposed for fire for a minute or so. You can not use this more than 10,000 yards from shore. If its good weather they will see you and get 15 minutes to fire on you . In most bad weather your torpedoes will be to inaccurate due to the platforms stability. In heavy rain conditions with a flat sea you will have a chance.
Im not satisfied with the fix ( if a players wants to run a daytime middle of the Ocean attack he should ,but 95% of the time all the boats will be lost for no gain) , but your arguments on guns having trouble to hit them are poor. The guns have enough training which should be obvious since they can hit much faster and smaller aircraft .