I'm not sure exactly what you mean by 'big experience'. The fact is, NOC 4012 is considered a skill level A, and it even has the requirements that one needs to be enrolled in a college or a university program before they can claim TA/RA work experience under NOC 4012.
About TA hours, I am aware that most of us are only doing TA for maybe 5 to 12 hours per week (which would out to be, as you said, around 60 to 130 hours per academic term). And I did not try to hide this at all on my work experience letter. I highlighted the fact that my NOC 4012 work experience is a combination of teaching and research assistantship, and broke down the number of hours for each academic term. I never claimed more than 12 hours per week for TA (after making sure there will be no contradiction to the number of hours given by HR).
As for RA, I always suggested people to only claim as needed to bring the total number of points above 67, and AT THE SAME TIME, to make sure that your RA rates won't be below the minimum wage of that particular province. Also, be mindful of the fact that you are technically studying full-time as well (which is defined by the CIC itself to be 15 hours per week).
If an average worker usually spends about 40 hours at work, what would be the issue in claiming that we study full-time for 15 hours a week, and work (which we are authorized to provided we have study permit and we work on campus) maybe 15 to 20 hours per week? Why should this be considered fraud or misrepresentation? Why is this claiming more than we deserve? If you claim this much, most likely your hourly wage will be quite a bit above the minimum wage of 10.25 dollars per hour.
And no, we don't work all the time. We need to eat, go to the bathroom, sleep at night, sometimes we need to work out, take a walk in the park, play with snow [and no, I don't like snow either], etc. That's why we're claiming we're studying 15 hours per week (hence, full-time PhD student) and working maybe 15 to 20 hours per week rather than 168 hours per week