Stadia definitely had software engineering related issues. The latency and stream reliability might have been better than competing services, but I found the UI and store to be quite lame. Features that were promised at launch (e.g. YouTube integration) took years to show up and weren't as good as advertised. Launching a game took too many clicks and way too much waiting. It should have been instant and that alone would have been huge. Porting games to Stadia was too hard leading to an anemic catalog; meanwhile Valve knows that the catalog is everything and engineered Steam Deck to run unmodified Windows game binaries on Linux! Google ultimately failed to take advantage of the unique advantages that streaming should have given them, and without any compelling unique features Stadia was just a worse version of consoles with a subscription fee.

The pricing model was probably the biggest single issue, but I believe better engineering could have made a difference.