If you bought a fridge that didn't keep things cold you'd take it back/complain.
If you bought a car that overheated every 10 minutes you'd take it back/complain.
If you bought a meal at a restaurant and your chicken was raw inside you'd take it back/complain.
If you bought a phone that refused to make phone calls you'd take it back/complain.
If you buy a flight simulator product and complain you MUST have an agenda and need to get a life.
If you bought the fridge, car, meal, or phone and they didn't do any of those things, then they'd be failing to perform the basic functions they're built for. Thus, you'd have reason to complain.
Lets see what the product description for the C-5M is, from FS Pilot Shop:
Different MDL files for FS2004 and FSX
Very High Detail Exterior and Interior
Photoreal Textures
Detailed doors and Cargo bays
2D Panel
Flight Manual
Paint Kit
Are any of those things missing from the product? Granted, your idea of 'very high detail' may differ to others', but to me, from what I can see on the screenshots, that VC does look detailed (can't really see the small details on the external, being such a large aircraft - perhaps that's one area they should work on). Added functionality like systems and clickable switches isn't mentioned, so I can't expect that from the product. So, I assume the product lives up to the description and the screenshots, and therefore if you've bought it, you've got no reason to complain about it, unless the addon actually doesn't work or doesn't deliver something in the description. You certainly don't have reason to send abuse to the developer for providing what they've said they're providing.
If you bought a fridge that looked exactly like the model in the shop, was reliable, kept your food as cold as it should, did everything Hotpoint told you it would, but then you complained because it didn't have an ice cube dispenser, then you'd look like a bit of a moron, wouldn't you?