You'll grow continuously without pausing at around 25,000 food per second. With max research (200 ms ticks) this is achieved at around 5000 food per tick. Going higher just stores it up, and it will continue to deplete even with negative food income, allowing you to focus on other resources while still gaining population.
I don't mean just to complain though. Really an incredible game, and once I got the hang of the controls it felt very smooth and fluid. It's nice to know you're going to read this, too. Kudos for really paying attention and responding to the comments, it's rare in developers these days and very welcome.
The "Ruby Tank" upgrade seems to do far more harm than good. The active skills all work by using a percentage of maximum BP, rather than a flat rate. By increasing max BP you in effect increase the BP cost of skills without increasing the rate you earn BP. The damage mitigation is nice, but doesn't make up for this. Unless I'm missing something, it seems like a better option would be to translate the percentage to what the flat rate would be at 150 BP, which you start with. So if Soul Tempest cost 10% BP to use now, it could cost instead cost 15 BP. It would still take the same amount of blood to earn that 15 BP, because the rate of you earn it doesn't change. It would function just like it says, by increasing the amount of BP you can store.
Have you tried upgrading sword skills? their BP cost gets lower when you do so. Also, Ruby Tank with Hagane Kegawa is a defensive combo. pair it with a good upgrade of Scarlet Synthesis and your BP problems are solved. also at what mode are you playing with? BP costs vary by mode.
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your insights are important info. i believe that will make me a better developer. Thank you for liking the game. :)