(I know this is a bit off-topic but I think ties squarely into the 'we can't use real life comparisons' topic going on because...)
For a giant to function they would need some new form of matter completely unknown to science. No metals we know of would allow a human-sized mecha to exist alone, yet alone a biological material. The bipedal body plan humans use is bad at big sizes. Really bad. The largest things on Earth are either in the water (which handles the weight issue) or had all four limbs for support, with a pretty regular feature among the largest groups all around being at least large, column-like legs.
Except Spinosaurus, but
we don't talk about Spino.
But basically the human bodyplan isn't the 'everyman' that RPGs try to present it as, its a very specialised body plan that's good at endurance. We're long distant pursuit predators when it comes to hunting because bipedality lessens the energy requirements for walking and running, letting us do it longer and just wearing prey down. Human stat bonuses should always be +Con if we're venturing anywhere near realism
.... Basically the realism stuff is never going to end well per the earlier stuff.