I designed alternators for Northwest Regulator (Specifically the Ford 3-G). Without having contacts in the manufacturing industry it is impossible to retain idle amperage and gain on the high end. Secondly, and most importantly I know of no OEM alternator that has enough area inside the alternator to house heat sinks large enough to offer safe dissipation of forward voltage drop of standard rectifiers.
So, despite the hype, despite any claimed warranty of a juiced up alternator, I would say ZIP THAT THOUGHT to any aftermarket hopped-up model. Marine models of hopped-up alternators count on a ONE HUNDRED DEGREE difference in engine room temperatures to survive. Stereo Competition units operate for MINUTES with the hood up -- not for hours in brutal summer heat. LESTEK changed their name, but was one of the few aftermarket alternator hop-up companies that knew what they were doing. I used to enjoy working with them.
Dedicated alternators offer lots of advantages. One being the ability to goose it with a frankenstein remote voltage regulator. The second being an ability to make it survive much longer by installing a remote rectifier assembly.
I own a pair of monster alternators. Both are goosed up. Both are equivalent to 800 amps (each one) at 14 volts. I had to convert this figure because few folks understand the mechanics of 28 volt conversion theory.
HAIRPIN alternators, offer the best idle speed performance. But the OP is absolutely correct about the chassis alternator and ECU. Can't play games when voltage and rotor field current is being analyzed by the ECU.
Quicksilver has my design remote rectifier that has a five pounds of finned copper remote rectifier. EACH rectifier and lead weighs TWO POUNDS. 1,270 amperes EACH at 1,675 volts PIV. The same rectifier is used on the Delco 50 DN alternator driven by the Lombardini air cooled diesel. Yet another of these rectifiers are powered by a charger in the generator room, but that one is a full wave single phase unit. Sheesh I purchased 5/32" copper back when it cost fifty cents per pound then silver soldered it plate to stacked plate, then had it hard anodized.