I would personally argue that the dramatic arc is about the structure and presence of those various components, not about the length or magnitude of each. Most games (although not all) feature "falling action" and "denouement," they are just very brief and wrapped up in non-gameplay elements, which is not actually out of line with the idea. These are not plays, divided into acts.

For that matter, in most games, especially RPGs, the actual gameplay isn't part of the narrative structure at all. You can essentially remove any time spent during actual gameplay and THEN build the structure of its narrative. The fact that there isn't gameplay after the "climax" (which is assumed to be defeating the final boss - this actually isn't always the case) is irrelevant because the narrative isn't told through the gameplay.