Most RC kits... talking anything from boats, cars, airplanes, helis and multicopters etc... typically will come with adequate but not great hardware. This is probably seen more in servos than anything often just being rated to withstand the torques they will encounter in whatever the maker considers typical use. These will often be plastic geared servos.
At the same time, we also have to deal with compromises for various reasons as well. Besides a servos rated speed and torque we also have to consider it's weight. Plastic geared servos weight less than a metal servo, this is more important in the flying vehicles .. but it is a valid spec that still needs to be considered.
We typically want to use the strongest, fastest servo we can... metal servos, for a given size will give us that but cost more and also weigh more. When and where possible, always try to use a metal servo. When that isn't possible, even if it's a cost reason... you still want to use the best one you can get or afford in order to keep them from breaking as often as their cheaper counterparts.