Right now, the best way to tell the difference is by looking at Dragon Quest XI *edit* Heroes.
This should say everything. Performance seems to take small hits on Switch, the shadows are harsh, the lighting flat, the textures are lower res, there is less foliage, worse geometry, ect. That's not to mention I don't really think Dragon Quest is all that demanding of a game, but more so than LCU and the snake game.
Although that probably is the best comparison so far (because there are so few), I suspect it's not a good one none the less as it's not a particularly graphic heavy game, and it gives me the impression of a lazy port, because they let the game run at around ~20 fps in undocked mode on Switch judging by digital foundry's performance analysis. (Runs at 60f on PS4). This is one of those games where framerate is important, so it's possible the game could have looked and run better if they put more effort into it, or even looked worse than it already does for them to reach a 30fps target for handheld mode.
I wonder how many, if any, graphically demanding game comparisons we'll be able to see in the future though.
It goes a little deeper than that, I mean it won't even be the exact same game on Switch at 720p and 30fps. There will be less effects, and more than likely a cut back as far as foliage, textures, ect. I honestly don't think we will ever get a clear indication as I don't think any third parties will ever take the take to properly port a massive AAA game to max the Switch out.
In some cases they could possibly solve it by just lowering the resolution and framerate. I wouldn't be surprised if that's all they did to a game like I Am Setsuna for example. But in other cases for more demanding games where they scale back the graphics to the point where the game the starts looking like a poor representation of the original game, you have to start manually removing objects instead that can be crucial for the overal game presentation as well, and even the functionality.