Well, it depends on engine vs video game size+quality you're aiming. If the latter is high but you don't have required engine and assets to create your desired video game, it would be hard to develop that game. OTOH if the latter is low and you have proper engine and assets, it might be easy. Easy doesn't mean it can be done quick cause you'd still need to actually do the developing part.
I could add skill to the formula above but I believe you get the idea.