As I wrote above, the CF EXPRES is not meant to identify who can do 19 or 50 push ups; it is to see who will likely die if they are pushed too hard. That is why they have their vitals taken before the test, etc.
That's not to say that you still shouldn't try 100%, because your staff will know if you quit before you're tired.
Sports (gym) fitness and working long hours of civilian labour are not really equivalent to the kinds of stresses you will face, though. I agree that some jobs are exposed to the elements and some jobs are stressful, but for the most part they all allow you to take a break when your body tells you that you've had enough.
What is great about the Army (and phase trg) is that you will be put in situations where there are no breaks, and you will learn that your body can go way past the point of thinking it should shut down, as long as your brain is motivated enough to keep it moving.
A person won't fail CAP because staff can do more push ups than they can; a person will fail CAP because they are on day 4 of an exercise and still ruck marching somewhere and decide that it's time to give up.
It is easy to be on a computer saying "I will never quit", but you are dry, warm, well-slept, not over-worked muscularly, and not under stress.
A follower has to keep themself motivated even when everything inside them is saying "stop".
As a leader, you will be faced with those same difficulties to keep yourself motivated, but you have to then look at a group of your peers - who are also suffering - and inspire them to carry out your mission.
It sounds hard, and it is. If it were easy anyone could be a leader in Army. But keeping the road to graduation difficult, it will mean something to you when you come out on the other side and I assure you that on grad parade when you hear those pipes and they give you the cap badge you've earned, you'll never be so proud of yourself.