Scaling up your game is likely to run well regardless as long as you spend even a little bit attention to the porting process. However, it will never ... ever ... look as good as a game that targets better hardware and then is scaled down. You will always be limited by some extent to the assets you chose to use for the lower performing platform. Monster Hunter: Rise is a great example of this. They increased some things that were feasible to increase, texture detail, effects, resolution, etc. But you can't easily create model asset detail, truly high fidelity textures (although AI is getting pretty good at this), for instance, without recreating the model, textures, geometry, etc. OTOH: if you started out with a highly complex model, it's far easier to scale it down to less complexity.
Scaling up, you have to try to figure out what can you add to the game and it's rendering pipeline without breaking it's rendering pipeline.
Scaling down, you have to try to figure out what you can either remove or reduce in detail to run on worse hardware.
The second is far easier than the first to achieve a certain level of graphical fidelity combined with good performance on higher end hardware. The first will never be able to approach the graphical fidelity of the second method while the second method can still attain the same performance level on hardware that the first method's game was designed around and potentially look better if the developer is particularly good at optimization and scaling of assets, similar, or if the developers aren't good at scaling down it could also be worse.
Regards,
SB
