Making Gold Rounds available for credits was a mistake.
This change alone created probably the biggest balance issue the game has.
Before tanks could be balanced around normal rounds. Be it weakspots or good (high pen) standard rounds etc. Very few people actually used gold rounds, so no balance issues there.
Once they made it available for everyone is were the problem started. Balancing gold rounds with credits does not work at all for the good/rich players. I can shoot gold all day long. I wont run out of credits. Therefore I can pen enemies much easier.
Others don´t have this luxury and still shoot normal rounds. Because of the "special" round spam certain tank types became obsolete and WG started the armor buffing. This made the gap between gold and normal round users even wider.
If you have toptier tanks not willing or able to shoot gold it will drag your whole team down.