I think I have an investment path that takes Tak'kan trade and is only 30k behind yours in total earnings by the start of the fifth chapter four investment phase. Here are the ProN returns (not including the ProN from the chest or Gawnfall, but including leftover discretionary funding).
Post-war: 2672.5k
Ch 4-1: 2545k
Ch 4-2: 3387k
Ch 4-3: 4107k
Ch 4-4: 4447k
Ch 4-5: 4497k
Investments before the Third Arclent War are the same as yours, except no Ardford supplier and no aid station. (In order to afford Gasm Falls in the post-war investment phase, I can have at most one of the following: cache excavation, Ardford restaurant, aid station. The above returns require opting for the restaurant. The aid station is then bought at the start of chapter 4, though I suppose it might be okay to just skip it. And Simon has to do without the +10 luck and agility, but they don't make much difference, really.)
Post-war phase: New Givini/Chalice States/Tak'Kan trade, Eustrin guild, succubus trade expansion, Min's trade route, Gasm Falls. (At this point I only have 2.5k left over, which is why I had to delay the aid station.)
Ch 4-1: trading pillars, Stineford bank, Stineford weapons shop, brothel reform, booze shack, Tradesmasher's guild, lonely sailor, orc merchant, Givini bank, succubus band tour, mercenary office, imp offices, aid station.
Ch 4-2: HQ stat boosts (military 20, magic 10, hospitality 7), airship fleet, Cee'Kan shipping, Givini tea house, Yhilin bank, Theltiar rentals, Theltiar flowhouse, Denmiel mushroom farm.
Ch 4-3: hall of mental strength, Givini smithing, Givini mage guild, Lustlord statues and temple, succubus tower expansion, Tak'Kan mine.
Ch 4-4: HQ stat boosts (military 25, magic 31), Givini ruins, all Kyangan investments except the smith.
The returns for this investment plan almost catch up with yours in phase 3, and are higher from phase 4 onwards. It does this without making any extra sacrifices in terms of optimal event outcomes. As an extra bonus, it earns enough Elleani RP that the second best result in the Tak'Kan council vote is good enough for a perfect Gawnfall, so is a good option if someone wants to research purity magic first for the Ginasta RP. (Getting 80%+ without orc diversification is still painful, as you have to prioritise one of orc pools or democracy or Tak'kan housing, and I think it would be better to just give up on the club and unneeded extra Tak'Kan tower score).