Sure, the sub destroys all the transports, and if the ftr hasn’t got a landing spot in range, it’s also going down.
You just have to make sure you don’t give your opponents this opportunity, it’s like leaving 1 inf in Berlin and complaining that people shouldn’t be able to land with 2 inf + 2 coastal bombardments to take all your cash.
edit: you should really do something about your keyboard, it’s pretty irritating and might get you banned. I understand you might be a little disappointed by the correct interpretation of the rules, but it’s no reason to shout about it in forums. If you really hate this rule, then make up a house rule and agree before you start a game to play with your house rule.