Just lately I got some brand name cables for my scopes/sig.gen., I haven't compared it at high freq yet tho, to those low freq. cheap ones. Actually i just tried repairing a cheap one, and it seemed to have aluminum wires welded to the alligator clip. The wires really did not want to re-wet with solder.
IDK much about transmission lines yet either, but the BNC cable with alligator clips should be some 50 ohm coax cable. So it's an inner conductor surrounded by an insulator and then an outer conductor. Scope probes are something a bit different, with a lot more DC resistance iirc, I should watch Dave's video again.
And for good coax, for some length, say 20ft (maybe it's way more), and upto 1GHz for something like RG-58, you might only loose 1dB of power to the cable.
And it's normally used for power matching, so the output impedance and input impedance between circuit's should be complex conjugates, and the real part of each should be 50 ohms. And then the coax in between them, is almost lossless, and the power is shared equally between the source and the load. But maybe at 1GHz and some length of good cable, you would have a bit under 1 half the power at the load, as a little does get lost in the cable.