I've not done a really heavily scripted call centre so can't comment, but my experience is training calls often seem harder. It's not that they're trying to fail you, but often throw curves in that generally customers won't, answer quickly - whereas real customers faff and go off on tangents. They know the script, and 'helpfully' guide you in ways the customer won't.
The customer doesn't know the script, and if you've asked a question in the wrong order - and the conversation flows more naturally.
Like training: Fake cust: Hi, I'd like to check my balance. You: erm, yes, (right need a name and dob) could you confirm...
In real life: Hi, it's Mrs dobson, can I check my balance. You: Hi Mrs dobson (check off name as done), no problem, let me just check.
I had stock phrases to fill time and narrated what I was doing. "Bear with me a minute" "let me just get that up/change screen" "computer's me just thinking"
Oh and everything was awesome, super, lovely, I think I might have played with magic at one point....