People on Reddit seem to agree , so let me share the idea here:

The biggest issue is inconsistency between pass-through and input only machines, because them working differently is what is really confusing.

So, make input only machines act as part of the pipeline as well, just like pass ...

TL;DR
Artillery shell trajectories should follow a ballistic arc, instead of flying parallel to the ground.

trajectory.png

What?

Now, I understand that perspective in Factorio is wonky by design, but I still believe that this issue can be resolved. My (poorly drawn) idea is as follows ...