Below is a picture of why I decided to avoid friction tape. This shows the wiring harness in front of the battery where the coolant overflow tank goes. The friction tape has fallen apart to about nothing. As I handled the wire, shreds of the tape were falling off. Granted, the car is 35 years old but the last ten it's been in a garage.
At this point my plan is to encase smaller wire groups, like in the picture, with split plastic wire loom wherever I can. I have a bunch of different sizes. Then I'll tape the edges with3M/Scotch Super 33+ electrical tape. For bigger wire groups, I ordered a roll of that Tesa fabric tape as it has good ratings (And Cordes' approval!).
In the meantime, I spliced about a foot of 14 gauge wire into the bad sections that led to my left high beam. I had clipped out the two wires with cracked insulation and thought it was 14 gauge, but it turns out to be 16 gauge. Whoops! Oh well, better a splice that's too big than one that's too small. I soldered it in place, put heat shrink over the splices and the pair of wires are going into a split wire loom so they're better protected from heat.