I think you raise a key point about theory of change and observed practice.
I think we're in a funny situation where maybe there are these tradeoffs in the abstract, but they don't seem to come up in practice.
This "funny situation" means that something is up with the theoretical model. If the tradeoffs do exist in the theoretical model but don't seem to in practice then:
Both of these would be foundational problems for a movement organized around rationality and evidence based practice.
To me, the question is "what are the logical conclusions that longtermism leads to?" The idea that as of today we have not exhausted every intervention available is less relevant in considerations of 100s of thousand and millions of years.
I agree. The debate would be whether to follow the moral reasoning of longtermism or not. Something that might be "awful for people alive today" is completely in line with longtermism - it could be the situation. To not support the intervention would constitute a break between theory and practice.
I think it is important to address the implications of this funny situation sooner rather than later.