@grenudi
UT, on the best-supported and highest-performing devices, offers a level of functionality that isn't available in the competing projects you mention (for which I have deep respect).
For example, the fact that a system works partially on over 700 devices is of no interest to the average UT user whose device runs the system fully.
As long as UT offers competitive advantages over other systems, it will continue to attract users, developers, and partnerships.
Your beliefs about Mir are incorrect, which means your reasoning regarding UT’s architectural “problems” is flawed.
Ubuntu Touch has advantages and disadvantages (as other concurrents projects).
Your tendency toward an ideal world where all contributions could (or should) be available upstream clashes with a simple reality: many users prefer a non-mainline device that works to a mainline device that doesn’t work fully or is too slow.
And that’s why Halium is useful (currently) and why some people support and use UT (or Droidian or FuriOS).
Endlessly repeating all the "negative" things you think about certain compromises UT makes or about certain architectural choices that have been inherited and retained for lack of a realistic alternative does not seem to me to be effective in this context.