Why not have premium tanks give free exp without paying gold?

ARGO: I was thinking about this a lot. What is really the difference between having a Churchill "per say" or a elited tank. Think about it for a minute. You go and buy a gold tank for gold, it is supposed to be a premium tank that gives you the ability to earn better exp and credits than other tanks right? So you then just like any elite unit tank you now must pay even more gold to convert your exp. Now any elited tank can do this too.
So here is an idea, premium tanks should automatically convert exp without gold because they are premium tanks and there should be a reasonable difference between elited and premiums. Now I know some may say "That's not fair, everyone would get one then" Yes I know, but I suppose they could make it so you get more credits but less experience than a normal or elited tank only that is that it's readily usable. Thus a reason for having or even keeping an premium tank.