68 Dart wiring questions

It doesn't get shared. People who have done the wire around report the ammeter shows no charging, but does show discharging during start up (or when the alternator dies). This proves electricity takes the route of least resistance, which is usually the shortest path.
It's better than the insanity but usually not neccessary.
What situation cause the battery to demand high current? And when those situations occur, should the driver know about them?
I can't answer that for others. But I think people should know that this is not a win-win. It's a tradeoff.

The fuse is also a tradeoff. it needs to be sized for the wire, but which wire? Normally one sizes for the smallest wire one wishes to protect.
What size fuse is needed to protect a 12 gage wire? But will that be too small to survive the short periods of high charging that can occur in normal operation? IDK. Lets look it up.

edit: here's what one person or group came up with, and extrapolating from it,
16 gage fusible link would be replaced with something between 60 and 80 amps.
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With the bluesea calculator, using worst case normal use as 25 amps for 20 minute, and no more than 8' of 12 ga wire, the fuse should be at least 31 amps. The closest glass fuse is probably 40 amp slow or fast. So I think that your scenario that the fuse goes quick and then the fusible link does it normal time to burn out is reasonable. The actual seconds it adds to the burn is probably not a lot. (That's not a recommendation to anyone reading, just an opinion)