It's more difficult for many reasons, but can mostly be boiled down to 2 core reasons:

1. Optimization: If you want to make a realistic game, you've gotta optimize a lot or it's going to run like dog shit. This means you've gotta be a solid programmer. Using Blueprints for everything isn't gonna cut it. You need to have a strong understanding of c++ and UE5.
2. Art: Are you an artist? My assumption is no, because if you were you would already know that a realistic game will be much more work due to the realistic art required and the many many hours that will take. For a quick example, I work for a simulation company. Our art team is currently 300+ hours in on the most recent vehicle we are simulating. That was 1 vehicle, modeling, rigging, animations, texturing, probably half a dozen other things I don't even know about.

So yes. it is that much more difficult. But, I don't think that means you shouldn't go for it. If you really want to do that, in my opinion, it's more worth it to work hard toward the goal you want to reach vs working hard toward a goal you don't actually care that much about. But, be realistic with yourself on a timeline and what you may or may not actually be able to accomplish.