Do the experts agree with this conclusion? What I plan to do with mine if all agree.
I'm not an expert, and I don't agree with the OP's conclusion.
First, the OP said he cut his fusible links. I would have never done that. Fusible links perform differently than fuses. Even though one can obtain high current Maxi fuses and ANL fuses that have the same ampacity as several paralleled fusible links, the types of circuits and loads where an OEM still installs fusible links to this day, despite the availability of other high capacity current limiting protection devices, should be noted. Typically, OEMs use fusible links in the starter and alternator circuits. Clearly, the OEMs must still have a good reason for doing so.
One reason that comes to mind is inrush current spikes. When the key is turned to start, as much as 2,500 amps of current can transiently pulse through the cables that feed power to the starter. That pulse cranking current is very brief in duration... instantaneous... but it is certainly enough to pop a fuse. A fusible link can tolerate a longer duration of high amperage transients, which eliminates nuisance fuse pops, and yet still provides protection against dead shorts.
The same holds true in alternator circuits that recharge the batteries. After being depleted from glow plug operation and cranking, the batteries are primed to accept up to 500 amps inrush current once the alternator is kicked on by the engine. Sure, the alternator may not be able to generate 500 amps, but depleted batteries will take all the current the alternator is capable of producing, which maximizes the current flowing through the wires protected by the fusible link. If those wires are protected by a fuse instead, then a higher rated fuse might be needed to prevent nuisance pops, and the higher rated fuse reduces the protection margin of error for the wire being protected.
More than anything, fuses and fusible links are sized for the WIRE from the power source servicing the equipment. Fuses and fusible links are not sized to protect the equipment itself... especially on high current circuits (as opposed to computer module circuits). So the gauge size and number of parallel fusible links, or the amp rating of the fuse selected, must be indexed to the wire being protected, not the load expected. If more load is expected, then the wire size must be increased, and then commensurately, the fusible link or fuses are then increased to match the higher current carrying capacity of the bigger wire.
The second thing the OP said in his conclusion is that the two 12 gauge fusible links were protecting an 8 gauge wire. This doesn't make sense to me, because a fusible link is typically 4 gauge sizes smaller than the wire being protected. So while a single 12 gauge wire is indeed appropriate for protecting a single 8 gauge wire, TWO 12 gauge wires would NOT protect a single 8 gauge wire. Furthermore, the factory alternator B+ cable is 4 gauge, not 8 gauge. Now, a 4 gauge cable can by appropriately protected by two parallel 12 gauge wires. I suspect that this is what the OP meant, but his conclusion does not say this, and therefore his conclusion cannot be agreed with.
Thirdly, the OP has selected a 150 amp rated fuse for his 4 gauge wire, a wire which his research found was rated up to 160 amps (assuming a distance of less than the width of the engine bay). Even while the 150 amp fuse is less than the 160 amp wire, the difference is still not enough to meet the minimum 15% derating of the wire, due to it being in the engine compartment exposed to high ambient temperatures. To meet that criteria, a 136 amp fuse, or the nearest down rated fuse, which is 125 amp, would have needed to be selected. And yet a 125 amp fuse might be more vulnerable to nuisance pops... which reminds us why OEMs use those short lengths of skinnier wires instead... aka fusible links.
It isn't just the smaller diameter of the wire that makes fusible links... it is the characteristics of the insulation... which is rated to have the wire inside burn up and separate within the insulation, without burning the insulation itself in the process, which could create a flame and source of ignition in the engine bay.
I upgraded my alternator to a 230 amp rated beast. I left all the factory wiring in place, untouched, as is, with fusible links intact. To handle the additional output of the alternator, I added two additional 2 gauge cables, one directly to the positive post of each battery, with the other ends stacked on to the B+ terminal of the new alternator. I protected each of those two new battery charging wires with a relatively recently designed (within last 10 years) Buss Marine Rated Battery Fuse. What I was after in upgrading my alternator was better battery charging, at lower rpm (idle). It has provided that. My current batteries are now in their 10th year of service, with no sign of weakness. I noticed an improvement in the residual charge of the batteries after the alternator and battery cable upgrade.