my last flights have all been with normal airlines
Norwegian (very cheap, inflight internet even)
Lufthansa
Vueling
In all cases, flights full and no overbooking (anyone ever heard about the European fines and compensation?). In all cases, when I come with luggage the stewards or airhostesses come up to help you to put it in the overhead lockers and even in the luggage hold without any extra charge or comments.
The last flight out was with Lufthansa (and had some 60 kos with me - no extra charge): they just started laughing when I told them I had 4 tins of olive oil with me to explain the extra weight.
Low cost - I think you mean low service airlines.
Come on, still remember discussing with some you CAN take an extra bag with airport bought cigarettes. Stopped when I asked them to call the Guardia Civil.
Know your rights ...