Then debugging a pipeline is as simple as dropping in IO.inspect between statements as it returns the content as well as printing.
thing
|> stage1
|> IO.inspect
|> stage2
It takes forever if your assets are large. Just serving random static files shouldn't take long.
> IO.inspect
It's nothing like a real debugger.
Are you using the Erlang :debugger module?
The only "problem" I see is that we can't set a breakpoint on the first line of a Elixir pipeline, but to see the value of variable from that line we can set a breakpoint on the last line of the pipeline. To see why that happens we can try stepping through a pipeline with the debugger: First "executed" is the last line of the pipeline, then the second line, then third etc and it looks like for the debugger the first line of the pipeline never happened. I don't think this is a big problem to be honest.
Inspect is fine as in Elixir you don’t have any hidden state. Use the :debugger if you need more than this.
You do this for legacy systems. New systems should not use Bootstrap, there is much better out there.
Given you haven't even attempted to explain your reasoning, I can't possibly agree.