I recently flew BR LAX-TPE-LAX. When checking-in the agents inquired about my carry-on baggage, and I naively showed them my rollerboard. Both times, the agents requested to weigh it and ruled that I had to check it due to weight restrictions. At the gate, I did not see anyone checking carry-on baggage for weight, so am I correct in assuming that if I hide my carry-on baggage at check-in, I can take it onto the flight?

I didn't have any other checked baggage and could have saved 15-20 minutes at baggage claim on either end.