Tech debt doesn't accrue because of fast feedback iterations. Tech debt accrues because it isn't paid down or is unrecognized during review. And like all working code, addressing it has a cost in terms of effort and verification. When the cost is too great, nobody is willing to pay it. So it accrues.
There aren't many features that you'll never touch again. There are some, but they usually don't really reach that stage before they are retired. Things like curl, emacs, and ethernet adapters still exist and are still under active development after existing for decades. Sure, maybe the one driver for an ethernet adapter that is no longer manufactured isn't very active, but adding support for os upgrades still requires maintenance. New protocols, encryption libraries and security patches have to be added to curl. emacs has to be specially maintained for the latest OSX and windows versions. Maintenance occurs in most living features.
Tools exist to produce extra productivity. Compilers are a tool so that we don't have to write assembly. High-level interpreted languages are a tool so we don't have to write ports for every system. Tools themselves are abstractions.
Software is abstractions all the way down. Everything is a stack on everything else. Including, even, the hardware. Many are old, tried and true abstractions, but there are dozens of layers between the text editor we enter our code into and the hardware that executes it. Most of the time we accept this, unless one of the layers break. Most of the time they don't, but that is the result of decades of management and maintenance, and efforts sometimes measured in huge numbers of working hours by dozens of people.
A person can write a rudimentary web browser. A person cannot write chrome with all its features today. The effort to do so would be too great to finish. In addition, if finished, it would provide little value to the market, because the original chrome would still exist and have gained new features and maintenance patches that improve its behavior from the divergent clone the hypothetical engineer created.
LLMs output react because react dominates their training data. You have to reject their plan and force them to choose your preferred architecture when they attempt to generate what you ask, but in a different way.
We can have better tooling for sharing apps than the web. First, it needs to be built. This takes effort, iteration, and time.
Second, it needs to be marketed and gain adoption. At one time, Netflix and the <blink> tag it implented dominated the web. Now it is a historical footnote.Massive migrations and adoptions happen.
Build the world you want to work in. And use the tools you think make you more productive. Measure those against new tools that come along, and adopt the ones that are better. That's all you can do.