Ultium is a sound concept but GM's execution has been terrible. I would equate it to Alfa's rollout of the Giorgio platform that went horribly, but if you think about it, it has parallels.
Have you not noticed that no manufacturer, not GM, not Toyota, not VW, ever rolls out a truly all-new car? When a new platform comes out, they usually carry over powertrains or pluck a newer powertrain that has been running in some other vehicle for a few years. Then, once they're 2 years in, there is an engine'/transmission update. You used to be able to set your watch to the "All new Camry with same engine" / 2 years later / "Camry gets all new engine" / 3 years later / "All new Camry with the same engine" cadence. The reason for that is that it is incredibly difficult to set up a whole vehicle platform AND engine / transmission platform all at the same time. The latest "all-new" CR-V came out in 2022, but the engine platform dates back to 2014 when it debuted in a mid-cycle refresh of an overseas market Honda Fit.
And that is why the Alfa Romeo Giorgio platform had so many issues at the beginning. The Giorgio, which debuted under the Giulia and later the Stelvio, was the first truly "all-new" vehicle we've had in decades. It was a new platform, on a new production line, with a new engine. The only off-the-shelf component in that car was the ZF 8-speed automatic. These days, Giorgio seems to be doing just fine as the Jeep Grand Cherokee and Grand Cherokee L
Now take that task and multiply it by 10. Not only did GM build a new platform, they built a new powertrain, and a new battery pack, and then they had to build the plants to build that battery pack, which they'd never done before. They called in LG for help, but it is still a massive undertaking.
The early Teslas were utter rubbish (some would argue they aren't much better today). Worse than anything GM is experiencing at the moment. GM, for all its faults, at least had the wisdom to stop production so the issues could be addressed instead of pushing out sub-par beta-test products like Tesla did. Keep in mind that the earliest Tesla Model-Ses are now 12 years old, one year OLDER than my Avalanche.
I've been in a battery presentation for Ultium, and I do believe that GM is on the right track. Their modular design makes it easy to future-proof the design for new chemistries as they become available. They'll get there, they're further ahead on the curve than Tesla was 12 years ago simply because, unlike Tesla, they can make a door that shuts properly.