I know I've had this discussion before, though I don't know whether I've had it with you specifically...
How, exactly, are you playing this game, where you actually need to spend all or even a majority of your minerals on warships in order to conquer something in the mid game?
When I beat the 5x grand admiral contingency and their >20 million combined starting fleet power, I owned over half the galaxy, and had a research nexus and a Dyson sphere and 1.5 - 2.5 ringworlds and habitats... I dunno, I'd have to revert the game version to count them but let's say 20-30. And had a fleet that gave me significant negative income out of port despite having something like 2000 fleet cap.
If you have so little mineral income that you actually need to spend it all on warships to win a war in midgame, you have too little, or you're spending too much of it on upkeep of warships you don't actually need.
In late midgame, I've got 10s of thousands of minerals I
need to spend on something. My limiting factor on rebuilding my fleet against the contingency wasn't minerals, but # of shipyards. My positive income was around 8000 after dealing with hub #2 (from a low of about -3000 when the crisis started), since my fleet was down to like 1300 cap and the ghost signal weakened. Since my net income kept swinging back and forth... Well, I had to go back to building habitats and ringworlds when it was high, or I'd cap out my 125k storage or whatever
Buuut... These are subtractive discounts. When you already have -40% from fanatic xenophobe, -20% is actually -33%.
My favorite game was a spiritualist fanatic xenophobe with parliamentary system, rushing all the outpost discounts. I had 213 systems before I even had to declare war; when an outpost costs 18 influence, no one can cut you off