Oh, didn't read you had a difficult time with it. I can copy paste my routine doing hardcore trav runs.
My hardcore ladder setup, merc does damage, i use war cry:
If i can afford: 2 x lem'd 6s cs, otherwise plain or lem'd baba blades
Wealth runeword
Cot lem, or kira lem or um for big resist boost
Chance guard
Goldwrap or goldfind belt
Infernostride or goldfind res boots
Goldfind rare amulet
Dwarf star
Raven frost for cbf, or another dwarf star if you choose to use kira lem
Merc:
Ebotd war pike
Fortitude, or wealth when you get efficient enough
Kira's guardian for big resist boost and cbf
Now to your points:
You use gavel of pain on switch. It is a big damage booster and gets your merc off to a flying start. War cry and amplify damage do not cancel each other out. So speaking to that point, my method of running gf in hell hardcore is this: Herd the members a little bit, gathering at least 4-6 in a bunch about 10-15 yards from the stairwell, then run down. But not too long or too much, just in a quick motion, otherwise it quickly becomes too risky. Run down the stairs, heal up. Run up again, immediately switch and cast amplify damage. Run 3-5 yards from the member pack, which the merc now has engaged, and immediately cast war cry repeadedly. The other members will usually start flocking towards your merc and yourself, and you will stun about 70% of them. War cry stuns the unique members 10% of the time, so they will be a risk factor, and one will just have to read the game, if they have dangerous auras and is overpowered, it is sometimes better to restart the game.
But, when you get the flow of it down, it is the quickest way. They are most often packed together, and with level 20 war cry, the stun lasts for a "stunning" ^^ 5 seconds. So even when the unique members are hit (10% of the time), they are no longer a risk for 5 whole seconds. With most the members stunned, the merc will have a free path to start eliminating them. When they are amp'd, he will kill even the unique members in 3-4 attacks, unless they have stone skin. But amp will also remove physical immune, so it really helps with that too.
It takes some practice, but when you get this routine down, it is very fast, safe and efficient.
I agree with your point on the merc. But wealth adds 300%, not 10-15%. Even still, a strong merc is very important, at least in hardcore, and of course always in softcore. Struggling and taking too long is both dangerous and tiresome, and probably as you mention is detrimental to the overall goldfind amount over time.
I personally like fortitude better, because the big damage boost, and also the armor boost from chilling armor, very much helps in both maximizing damage from amplify damage, and helps with physical damage. The members can deal quite obscene amounts of physical damage, sometimes they have might aura, sometimes fanaticism, and sometimes both. In those cases, at least in hardcore, and maybe even one of those two in combination with conviction aura, makes it too dangerous and it is better to restart.
I have read about people even switching the weapons, and help deal damage with the barb, speeding up the runs even further. I don't know if this is worthwhile.. switching to goldfind weapons when using find item. It is an interesting thought.
With this setup, and of course with inventory filled with 30-40% gf charms and a good gheeds, i managed to get 500 000 - 1 500 000 gold each run, and an estimate is maybe one run every 2-4 minutes, included sorting through the items. I am still debated on picking up items worth 35 000 gold, but i do pick up small items, like orbs, wands and sometimes knives which can spawn with charges, which gives good prices. I usually don't bother with armors, unless there is only one or two.
The ladder season i ran gf barb almost exclusively, i ended up with about 25 000 000 gold to sell in the trade room, and probably gambled about 100 000 000 gold. I gambled a perfect metalgrid ^^ That was crazy. Among other decent rares and such.
So gf barb is definitely among my top fun builds. But it requires good gear and practice in order to be efficient.
D2:R