okay, let me explain why this doesn't work.
let's say you start as a herald and multiclass into fighter. okay, your exertion pool is equal to your PB. now let's say you start as a fighter and multiclass into herald. okay, your exertion pool is equal to twice your PB.
this is the inconsistency...
i consider muskets and pistols a little early for steampunk. i usually consider steampunk arms to be more late victorian - repeating rifles, shotguns, revolvers, and weird steam-powered contraptions.
if you get a regular exertion pool you can't get another. so if heralds get a regular exertion pool then a fighter dip doesn't give them a second, even if the herald can spend exertion to cast herald spells.
not a major one, just that it kind of removes some of the herald's identity with its...
unfortunately this creates the same problem as the exertion being on a long rest in that now you have to create a multiclassing exemption again so we're back at square one.
that said, pb*3 is much less of a problem then converting the spell slots you'd have into exertion to be regained on a...
i was mentally including saves under proficiencies, but fair enough to spell it out.
i think the easiest way would still just be to change how maneuver degree progression works with multiclassing.
there's also the warlock's spell point values, which would probably work better for a proper half...
do you mean in terms of proficiencies? proficiencies do interact kind of weirdly with multiclassing, that is true, but they're their own thing separate from most other class features.
the problem with reducing exertion from a fighter dip is that the multiclassing rules exist as is to prevent multiclassing inconsistency. the way @Anonymous3 worded that change, starting a ferald build with fighter would be even better then RAW because you'd have fighter exertion, herald slots...
i don't think that works raw (it's not damage)...but i'd roll with it. that's wild.
i never even CONSIDERED making spellcasting squads. which is crazy, because i've considered making airships that fly via multiple casters concentrating on a rare fly spell to make it float. that's a whole other...