Even if you accept that "web" is niche (which I don't), and all your input is trusted not to be malicious (which is not necessarily true for non-web applications, especially if they are privileged), you still need to worry about input with special characters causing bugs. Web apps don't have a monopoly on using a database, or generating strings in a specific syntax that includes user input.

With respect to compilation, that is basically is how t-strings work, but it is the python interpreter that does the compilation. When it parses the t-string, it compiles it to (byte) code to generate a Template object from from the expressions in scope when it is evaluated, which may happen more than once. And if you really want a template that is a separate object that is passed the values separately, you can just wrap a t-string in a function that takes the parameters as arguments.

> two dozen templating libraries that offer much more comprehensive safe and fast text-generation solutions than what t-strings do

But t-strings allow those libraries to be safer (users are less likely to accidentally interpolate values in an f-string, if a t-string is required) and possibly faster (since the python interpreter does the hard work of splitting up the string for you. t-strings don't replace those libraries, it allows them to be better.