MH152
You've hit the nail on the head. The attitude of many flying instructors is "It'll be alright there's a big safety margin." The student thinks this is normal.
I learned to fly in a C152 and occasionally an aerobat with even less available payload. The instructor & I were nearly 30 stone between us. With full tanks we were well overweight but the little 152s flew perfectly.
I have since discovered not all aircraft are so forgiving.
DO