I think the issue here is less the being able to place units you buy, and more the exploits that become possible by buying a unit you never intend to place.
For example, if I buy a CV on a UK turn, I can hypothetically fly a FTR from Moscow to attack a German Navy in the Baltic Sea, even if Karelia/Norway/Germany/Poland/Baltic States are all German-owned, because I can hypothetically land those FTRs in the SZ adjacent to the Baltic Sea and UK during NCM. However, as is, I can carry out this attack even if it’s a blatant suicide mission, because as soon as the FTRs are dead I am no longer obligated to place the CV I bought earlier, meaning I can save placing it for next turn, effectively giving UK 14 free IPCs towards their next naval purchase and denying Germany a chance to pounce on a vulnerable CV for free value.
EDIT: Thanks for the clarification @JuliusBorisovBeamdog. Glad to see you and the team are still working hard at making improvements. The game has come a long way since launch quality-wise and I’m sure everyone here appreciates the continued dedication.
EDIT #2: I guess what I’m saying is that the purchase system should be left as-written in the rules. Players should be punished for bad tactical decision making. Otherwise all games would just come down to a combination of luck, basic knowledge of the map being played, and which side the map being played is biased towards. It’d be more of an exercise in optimization than an actual game.