I could even just convert all of my resources to credits, and buy whatever I need whenever I want it.
This isnt really true, the difference in the sell and buy prices and the low volume for anything other than minerals means you can neither liquidate all your resources or buy them back when you need them.
e.g if I sold my stockpile of XUH2O on shard2 the best price I could get right now is 0.01 and if I wanted to buy it back it would cost me 2.249 ~ 250 times as much.
However, terminals do allow you to move almost arbitary amounts of energy, minerals and boosts around your empire. Meaning that rather than draining a single room of resources you need to drain the empire.
But the reality of it is that most players do not have defense code that is unbreakable without draining.
IMHO the terminal does simplify things too much, it makes it too easy to move the resources to where they are needed. I think a terminal blocking capability is exactly the type of ability a power creep should have. I.e. its a very powerful ability but not one that is going to win a battle without other creeps.