If you get a new commander, and you have to learn the abilities which is not a problem. You upgrade that ability and it costs you credits, not a problem. So to learn the first ability costs you 100 credits, if you want to upgrade that ability it costs 300 credits. Not a problem. But if you go to learn a new ability it costs you 300 credits
You might argue to learn the most powerful ability costs more credits, but I am talking about basic ones as well, at the lower levels.