So yeah, it Oklahoma, Arkansas, Louisiana, and most of New Mexico sent all their power to Texas nobody in Texas would have lost power. Just everyone in all those other states.
Simple proof, no where else in the US or any other developed country does such a situation arise. And even most developing countries have better connected grids. When southern Australia didn’t, it paid for that in rolling blackouts.
And once again you're just ignoring that pretty much every state even near those other states were also near their breaking points with many of those areas having rolling power outages at the time. It's not like the storm was only hitting Texas.
When I say "most the other states", I'm saying most the other states combined. The shortfall alone was more power than several average US state generating capacities put together.
The reality of Uri is that the neighboring regions to the north (SPP) and east (MISO) were on the brink themselves (grid emergency and rolling blackouts in SPP), and the import capacity from their neighboring regions (i.e. the midwest) was constrained; they couldn't import more power from their neighbors. If Texas were part of the Eastern Interconnection AC grid (i.e. connected to SPP and MISO), I think fewer people in Texas would have lost power and more people in Oklahoma. SPP and MISO just didn't have any more power in those areas to ship them.
SPP & MISO have been interconnected with each other forever, they're on the same AC grid. But the capacity between their systems is limited, hence the blackouts in SPP. They just never bothered to build out the capacity because it hasn't made a lot of economic sense. I think that's the best counterfactual example of "what would have happened if Texas didn't have their own grid", and it suggests that the storm still would have been a problem.
SPP had generation issues like Texas because of the massive drop in natural gas supply coupled with high demand and had rolling blackouts as well. MISO was the most impacted part of the country weather-wise and had practically no spare capacity, and PJM was also still under very heavy load.
You get far enough out and you start realize the rest of the country isn't a single grid. The east and west aren't very connected, and from the central US to the east there's really a few different grids with interconnections, which were all getting maxed out without trying to take on the shortfall in Texas.