Bypass ampmeter through bulkhead

Ok. It depends on what you beleive.
How much current does the battery draw? and for how long?
How much current do the other items draw? and for how long?

So it comes down to the condition of terminal P, how many accessories are going at once, and how long they are on.
A headlight relay system diverts a 9 to 12 amp draw so it never goes through P.

The direct wire from alternator to battery is easy. But.
What happens or has happened when the battery is drawing 10, 15 or more amps for long periods of time? Do you want to know that? A voltmeter will never show that unless its due to a regulation failure. Even then it may not show high voltage if the failure is a poor connection in the ignition-field wiring. Both voltmeters and ammeters are useful, but they show different things. That's not bad or good, just tradeoffs.

Yes. Using the alternator while driving to recharge a battery that has been run down can cause the connections on that circuit to see higher currents than normal. That certainly can cause heat damage to all connections on the circuit. The direct connection from alt to battery protects the connections against that situation. However that may not be the only damage done.

Why has MAD made the ammeter the bogeyman? What is the example they use? Was that the battery or the accessory that caused that much current? I think the answer is in their own text. They wrote, wrongly, that all power for running the vehicle comes from the battery through the ammeter.