There are levels of scratchbuilding.
Pretty much any one of us can take a few pieces of sheet styrene and make a scratchbuilt hood scoop. Pretty much any one of us can scratchbuild a roll cage out of aluminum or plastic rod.
But not many of us (maybe none of us here?) can take a few sheets of brass, some aluminum and brass wire, rod and tube, a few chunks of aluminum or brass, and various other raw materials and create a complete model car from those raw materials. That level of scratchbuilding is definitely above and beyond simple kit assembly, or even kitbashing. That level of scratchbuilding definitely requires a skill level above that needed to merely assemble a collection of individual kit parts, so yes, true scratchbuilding is a step above model kit assembly.