This is the cultural differences between the west and Japan. Japanese people really likes big robots but the west just doesn't buy that concept. Therefore early big robot anime didn't really made it into the western market. It's only when they started reducing their sizes (astroboy, I mean, is it even a robot?) that it started to get popular.
Early on they stole a lot of artwork from Japanese products, so the Phoenix Hawk, Stinger, Wasp and especially the Hatamoto-Chi are very much the Samurai with wings thing. Also, melee combat was a significant part of the game, mechs carried swords, axes, clubs, and those with fists could punch. Even the weirder 'Mechs of this time were described as more insectoid or bird-like, like the Locust.
They trended toward more mechanical, military machines as they hired artists and did their own designs, they trended in a more mechanical, angular, military vehicle direction and more often than not used backward-kneed legs. Look at the Timber Wolf or the Shadow Hawk. Even when the 'Mech was more humanoid and had forward bending knees they tended to be more angular and mechanical like the Summoner.
Pictured above is Clan Smoke Jaguar's invasion of the Draconis Combine.
And those are just suggestions. Your mech, as long as it conforms to a pattern-group (read: has bits from one license or another) can look like literally anything. Wanna play a Tokugawa but it's Blade Liger? You can do that. Wanna do a Sunzi that's literally Big O? Go for it.
Exactly! When I ran a game for a few of my friends, the art they chose for their mechs included some Gundam-ish stuff, an official bit of Lancer art, a tweaked version of an official bit of Lancer art, and just a plain old AT-ST