Suggestion for unique soldiers

Does anyone else hate when you have a rank 1 infantry man unique soldier but you the rest of your soldiers are rank 3-4? Well I suggest a way to fix this problem and make unique soldiers still useful.

An upgrade system you pay idk 10k silver and bam your soldier is now rank 2 or higher and can still be used in better squads. This will eliminate having 1 soldier that you only have in your squads just for extra xp but can actually use them.