Personally i've no problems with the unlock concept but I see and I know lot of people complaining about this part of the game. For myself I think the major problems with this unlock system is not his existance but the way it is presented inside the game and especially inside the campaign. Let me explain myself... Currently for unlocking some additionnal parts of your plane you have to select a plane, play a mission and win points for this plane until you unlock the item you want. But something is missing here !
Actually you don't want to play the campaign for a new item, you want to play a campaign to learn from the game how to use this new item ! Clear example : I want to unlock a new canon for the lagg-3 and I want this cool "37mm Sh37" canons here but "hey" expect if I google it I don't know what it is and what is it for ??? And that's exactly the point here, this game is so intense and he wanted to be so historicaly accurate but when it comes to teach something to the player there is nothing. Of course there is lot of experienced pilotes here which already know everything but there is a lot of new pilotes too like myself and we don't want to be throw in the deep blue sky of stalingrad with nothing. So this is how it should be : The current system with points of experience linear to the historical conflict can be kept it work pretty good but only to unlock skins which are less importants and where no instructions are needed ! But for the planes and their parts it definitly must be some missions dedicated to their unlock, where inside of the mission you learn how to use the new materials you want to unlock and if you complete the mission it means you know how to use this new planes or new canon for example and you earn the right to use it, like some sort of exams !
So to sum up make the work to unlock then usefull it will be less painfull and more enjoyable for everyone and it will make the players experience much more immersive !
PS : I want to learn how to use this