Different sizes of artillery is quite plausible Jayson... Take a look at the military, especially look at WW2... The variety is staggering, as the need for variety changed as the war progressed. WW1 as well... Artillery isn't the same today, but one could imagine a fictional war like in SW, artillery differences are likely.
I'll readily admit I'm happy to rationalize it though, to like the toy better.
It is grossly underscaled compared to what it's based on though DR, your'e right. Some customizing might make it more plausible as an anti-tank type weapon like a PAK from WW2... I think it has potential for sure, but for my tastes it may take a little customization for me to finally be totally happy with it.
It's like the AT-AP... Some of the features are scaled down on it, and those just look bad.