It really depends on what type of game the gambling is taking place on(dice, crash. ect)
if its one played against the house and not other players i think its both luck and strategy in a sense.

Ultimately it is more or less 100% luck but you can employ different strategies to have a bit more control over the luck. more often than not that will work for short term sessions but luck being luck if you push it to far in one go without changing things up you will most likely rip as the variance comes to bite you