this looks ideal for sweep3rail. no such command.
Loft says all to be closed or open.
I close the rails and get a mess.
such shapes are never the demos of a few wavy lines and loft command I see.
what command sweep3 rail.3dm (38.5 KB)
another simple shape for sweep2rail yet having adjusted the node I get a warped face.
sweep2rail twists.3dm (27.4 KB)
you will generate overlap there since the “rails” are intersecting each other
I would focus only in the top surface instead of using the closed triangles. the other 2 surfaces could be just extrusions.
and this for the other example
There’s been a “Multi-Rail Sweep” on the Wish list for some time.
Generally, there are work-arounds for specific situation, but it’s there.