Not to be flippant, but cosmology is essentially the science of dealing with these kinds of scales. It’s an entire field whose goal is to make questions like the above tractable.

Completely agreed. In the era of concordance cosmology, one can, if desired, use the relative abundance of the elements, the distribution of galaxies in the sky, and the distance to far-away supernovae and, with two free fit parameters (dark-energy and dark-matter density) predict the properties of the Cosmic Microwave Background anisotropy.

It's an incredible fact that one can do this -- predicting the properties of the photons emitted at the very first instant that the universe became willing to allow a photon to propagate freely.

A young Randall Munroe could have picked from a number of really well-motivated reasons to state, "Science, It works...", but he picked this one: https://xkcd.com/54/

Modern precision cosmology works really, really well.

Props for the first xkcd link I don't feel like I wasted my time clicking.

That’s a very good point, and obvious when you point it out.

Still, I have a sneaking suspicion we are making flawed assumptions because our observations are from this point, and only this point, in space and time.

Just my opinion, and it’ll probably turn out to be flawed itself like most of my opinions ;)