<Snipped quote by Silverwind Blade>
Sorry, I'm evaluating. In Macross, the mecha are so tall because the aliens they're fighting are that tall, too. 18-24' mecha are better off than 40' mecha, but still have pros and cons.
They have pros and cons, yes; if you're evaluating them as a real thing.
But this is a setting where they
do exist and are used commonly, frequently, and effectively.
It's about suspension of disbelief and embracing the conventions and themes of the setting. If you're expecting it to follow and adhere to realistic physics, or consequences or whatever else - then you're probably looking at the wrong game.
Need I point out the facts that the setting also is one where there was a dimensional collapse and multiple worlds crosssed over? I'd say that's more far-fetched and unlikely than the fact there's 25-foot tall combat mecha.
'Realism' is hardly the point - it's about escapism, enjoyment, story-telling and fun.
Embrace the setting and the genre for what it is - not what it isn't.
Finally, embrace the setting. I have seen real robot mecha-themed anime in the past where people have got spectacularly stuck on the 'real' part, and not the 'anime' and 'sci-fi' part. The plot is king and the story is the point. Dramatic licence and tension will always win out over the 'realism' of the setting or the scene, because that's what the point is. And really... this is a setting where multiple dimensions have crashed together, and various species and races of people pilot bipedal giant robots. Realism isn't exactly in massive abundance, so trying to explain away every piece of scientific and technical information just... isn't the point.
Getting into the minutiae of the tech isn't the point, and isn't the goal.
Quoted from my opening post about the RP and the setting.
Honestly; if you're not excited enough about the idea of piloting a cool mecha in a semi-apocalyptic world where you can be any one of a number of different species or races - including ones you make up yourself - and fighting against anything from other mecha, to genocidal robots, to rampaging dragons, then I'm not sure what else will convince you?