"the effort needed is unlikely to be worth it"
--> u just have not to block theses countries , it takes 5 minutes to do it.
It is true that it would be fairly easy to make these countries accessible by removing the neutral hexes but that would create an unhistorical situation. I do not think that they should be made empty and accept the Axis troops and air units without resistance as historically they clearly opposed an alliance with Germany or the Allies, hence they remained neutral. Which means most likely they would have opposed any nation that violated their neutrality. As it happened with the Netherlands, Belgium or Norway, to name a few.
"Also, you can never buy ships of any kind in Panzer Corps in general. Why would you expect the mod to suddenly allow it?"
--> i don't understand why you are speaking of the vanilla game . A mod is made to change the original game! In 1941, Hitler could'nt build destroyers? historically, it is nonsense.
Historically only a few German destroyers were commissioned after 1941. From mid 1941 German ship building almost exclusively focused on U-boats and to a smaller extent on some other smaller vessels like S-boats. To represent the few new destroyer (and torpedo boat) units one (or potentionally another) destroyer unit appears in the map in 1943. And in this mod a destroyer unit represents a flotilla of 8 actual destroyers (or torpedo boats, corvettes, frigates and similar escort vessels). So these are basically covered.
Also, as written above, building a destroyer took some time. For example in case of the German "Type 1936B" destroyers their construction tipically took one year and then at least another before they were commissioned (after being fully equipped, tested, trained, etc.)
And obviously, the construction of larger ships took even longer. In the case of battleships around three years. Therefore, in the time frame of this mod it would be unrealistic to be able to purchase new naval units in just one turn, which takes two weeks.
he can't send paratroops beyond ennemy lines in england or in russia, (or even in greenland! )
The Ju 52 had a maximum range of about 1000 km or 600 miles. So there was no realistic chance of an airborne invasion of Iceland (as it lies about 1500 km from Norway), or a deep penetration behind enemy lines in Russia, even if there were more paratrooper units (and also Ju 52 planes) available. Unfortunately, PzC does not simulate it very well as air transports use no fuel and have unlimited range and I was unable to fix it as it is hard coded. But the fact that there is only one paratrooper unit available makes it fairly historical as it significantly limits their operational usefullness as it was indeed the case.
Additionally, having more paratroopers would make the mod much easier as the player would be able to paradrop several units behind the back of the enemy and the AI would be unable to realise this threat and to deal with it. The game also does not have a very good supply system and would allow a large number of units being dropped far behind the enemy lines and operate isolated with no problem when realistically they would not survive for long without sufficient supply lines.
he can't attack by another way ( like by turkey or swis or south france )
Although these neutral countries have to be avoided, currently there are many alternative history options available, including the naval invasion of England, Northern Ireland, Iceland, Malta, the Near East or crossing the Black Sea to reach the Caucasus. And none of these happened historically. Even the invasion of England provides several alternative options and routes which can be tested.
he can't take gilbratar
Actually it is possible to capture Gibraltar, at least theoretically, from the sea. If I remember well a few players did so before. It is also possible to block the strait with naval units, especially submarines, which may be more cost effective.