Covid-19 might have meant more exposure than usual to the All Blacks over the last two years for the Australians, but it provided an opportunity to learn against the best, he said.
"We're not where we want to be," Rennie said.
"It's easy to look at the scoreline, isn't it? We gifted a lot of points; a couple of more intercepts today, we gave a couple away the last Test.
"I feel like the scoreline the last couple of weeks hasn't been a fair indication of where the game's at, but that's just the way it is.
"You've got to deny them opportunities, you've got to defend for long periods, and you've got to be clinical when we get our chances.
"I have no doubt our attack has grown a lot throughout that period, and it's fair say what others have been saying, because we're playing a bit of footy if you turn it over you can get exposed. That's the balance of our game," he said.
Rennie wasn't ducking away from the challenges ahead and said their next two Tests, against the world champion Springboks, would help Australia in the longer term.
"It's brilliant. It's what we want, and what we need.
"I came in with my eyes open, and we've got a lot of good men who are working really hard.
"We've had seven Tests against the All Blacks.
"Ultimately, I think that's great for us. We're learning quickly.
"We've got the world champions coming out for a couple of Tests, that's going to be great for us as well.
"But, look, we've got to be better at putting ourselves in positions to win these games.
"We've got to be clinical, we've got to look after the ball," he said.
There were too many turnovers after tackles and there were times when they were reluctant to kick while when it was on to kick with the All Blacks squeezed up and no one covering behind, they didn't take that option.
Rennie said he was enjoying the challenge of playing the best teams in the world.
"I have no doubt we're going to learn because the All Blacks are such a good side, and we're relishing the opportunity to play against the Springboks," he said.
They will be defending a winning record at home since 2014 against the South Africans.