Hey /m/, I confess that I'm not that familiar with mecha

Heads up, anon. You're not going to get a 100% foolproof, unattackable reason why mechas are being used. I suggest just accepting that unless you're going for the most gritty and down to earth interpretation, mecha aren't going to be one hundred percent realistic.

However, you can still look for explanations that hold up within the universes that have formulated them. I personally don't know much about Patlabor, but I think it explains mech with some pseudo-realistic justification.

Gundam- At least the Universal Century- Goes out of its way to justify mechas as being developed for space operation, with the limbs being used for flight adjustments.

>>15046511
Oh, yeah, I don't mind it not being justified within our universe, but rather how writers have incorporated mechs into the universe be it as a military application, or a requirement to fight aliens, etc.

In the meantime I'll start researching Patlabor.

I've never really followed Gundam but I find that curious as the mechs seem distinctly humanoid. I'll read up on the in-universe "origin stories."

>>15046577
Heads up on Gundam: It's basically a franchise with different universes that share some aesthetic and thematic points, so the origins and raison d'eitre of/for mechs are pretty different, or sometimes jut not touched upon.

Another anime that has an interesting take on mecha is Code Geass. The mechas there basically started out as semi-autonomous escape pods- Evolving overtime to become fully fledged military and civilian tools.
Shit unfortunately goes full on mecha escalation, laser-swords-and-prototypes-for-everyone in S2 tho, which is a pretty huge disappointment considering the way they portrayed mechs in S1.

In Gundam there is an elementary particle called the "Minovsky" particle. Which is produced in the reactors that power pretty much everything. When these particles are released they align and expand creating an "i-field". This field of particles will disrupt microwaves, radio waves, and damage exposed electronics. Because of this the i-fields are used in combat, effectively making long range guided weapons unusable. The mobile suits were an answer to this, they are an agile close-range combat unit that could easily fight within i-fields.

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>>15046266
Gasaraki has a pretty interesting explanation for the mechs in it. In just about every scenario, they're treated as extremely realistic weapons that are meant to dominate in close quarters urban environments by outmaneuvering armored vehicles and packing more firepower than infantry. This is only possible because the artificial muscle used to make this type of maneuvering possible is actually cloned from an ancient biomech created by ancient aliens that doesn't necessarily follow regular physics. And since this stuff is in all of the modern day mecha, they can actually move well enough to be plausible weapons.