Take a look at how much trouble the author had finding a working ST, despite there being widely published and used libraries at some point but which no longer work in newer versions of Coq. The author ended up using a very specific git hash version of the Iris library, and he admits the documentation of Iris is pretty much non-existent.

This doesn't inspire confidence, considering this author is also the most familiar with Coq of the three. He also somehow claims that Coq is stable, which I can only take to mean that it won't crash rather than that it largely preserves backwards compatibility given his difficulties. If we can't rely on some measure of backwards compatibility so we can build on stable libraries, theorem proving simple won't scale any more than programming of any kind won't scale in the same circumstances.

The number of lines of code required for the second task also doesn't inspire confidence that theorem proving with Coq will scale.

So I frankly can't see any reason to think that Coq even with tactics is a viable approach to real world verification beyond exploratory toy examples. No doubt we have different goals in mind when it comes to verification/theorem proving, which is why you think Coq is suitable and I do not.