If you take all the mass in our universe and run it through the Schwarzschild equation, you get a black hole with about the same radius as our observable universe.

Things don't need to be tightly packed to be a black hole, there just needs to be enough stuff in an area.

There's also been some major leaps in dark matter physics in the last few years. Revisiting primordial black holes using lasers and microlensing might actually be able to get supporting evidence here before long if the hypothesis holds.

PBS Space Time has a good video breaking this possibility and methodology down.

https://youtu.be/wh75ubECL8I

Difference being that we understand dark matter exponentially more than dark energy. We can actually observe it's gravity affecting light.

We're not stuck in here with them. They're stuck in here with us!

Scientific American points to an important fact.

"With our latest surveys, such as the Dark Energy Spectroscopic Instrument (DESI) and Euclid, by my very rough estimation, we’ve taken pictures of somewhere around 100 million galaxies out of the two trillion or so estimated to exist in the entire observable universe.

Shamir’s paradigm-shattering conclusion relies on 263 of them."

They are discussing bias in the selection.

"Unfortunately, this kind of extreme selection introduces many opportunities for bias to creep in. When we test a new idea in cosmology—indeed, in all of science—we work to make our conclusion as robust as possible. For example, if we were to change any of these filtering steps, from the selection of survey region to the threshold for deciding whether to include a galaxy in the analysis, our results should hold up or at least show a clear trend where the signal becomes stronger. But there isn’t enough information about such methodological checks in Shamir’s paper to make that judgment, which casts doubt on the validity of the conclusions."