Combat styles serve unique purposes
Every style is different and barely any are objectively "superior" to others if you don't compare them on specific aspects.
Modern Judo is about control
In modern Judo the idea is not to break all your opponents bones or kill them. The purpose the techniques serve is to break balance and use the opponents own force to bring them to the ground where you immobilise them. Especially the "ground combat" is why many martial artists train Judo at least to an extent as few combat styles covers this topic. Also it includes basic techniques of how to fall without injuring yourself.
Regular Boxing is about getting the most impact from your punch
A Boxer mainly trains for stamina and muscle buildup to give the punches a significant impact. If you have ever seen a boxer fight a regular dude the fight lasts one punch until knockout.
Taekwondo is about getting the most impact by technique not by brute force
Martial artists of this types often look slimmer than regular boxers for example. They fight completely different, but the techniques serve a similar purpose. A Taekwondo-Kick has a huge blunt force impact that can quite easily break bones.
Wing-Tsun Kung-Fu is designed to fight against physically superior opponents
By physically superior I mean people who are taller and stronger than you are. The style is all about balance and not ever holding up against force, but to use quickness and (your own) body control to have the opponents strength work against them. It is heavily aiming for weaknesses and does not rely on brute strength at all. I personally know women of small and slim stature that could defend themselves against a taller, physically strong guy if they had to. Even the basic punch is designed to work by quickness instead of muscle strength.
Krav Maga is designed to be efficient and quickly learnable
Krav Maga has a unique design philosophy. It is all about being simple and efficient. A person can get a 3 week boot camp of Krav Maga and would beat people who trained most other combat styles for a year. That is why it is so popular with military and the likes. The idea is breaking every situation down into abstracts and training reflexes on how to react. The combat style is taking lots of things from many other styles. It is more focused on strength than finesse, but it is efficient enough to be used by people who are not that strong.
Depending on what you want to achieve with your style it has to be specifically designed for that.
In your scenario that means giant vs human - from the giant perspective.
Using range to your advantage
As Aify pointed out in his answer you need to use the range advantage. Any punch against a human less than half your size would require you to bend over making you less mobile. So punches are entirely off the table.
The range of kicks is significantly longer than the range of punches. And another bonus is that kicks come from the hip which is closer to the opponent than your torso and shoulders where a punch is directed from.
Humans can only attack your legs and that only if you kick directed at them or they are very close to you. Defending against kicks is extremely difficult for a human in this scenario. The giant has significant force and being hit probably means you're thrown away. So their best bet is dodging. That is why kicks should be designed in a way that does not make you move towards the human during the kick in case they should manage to dodge. That would open a window of opportunity for them as they bridged the distance and have your leg at their disposal.
Another part that should be taking into consideration is what to do when the opponent managed to get close? Kicks do not work close range as you do not have the distance to create the impact you desire. So you need to use something else. As we have established punches are not useful either. But the giant also has a mass advantage. Simply trampling onto the ground (or the opponent) has a huge impact when you weigh more. In human combat trampling can only be used on enemies that fell to the ground. But a giant could use that on a standing human.