My suggestion to reduce the need for save scumming: have the Victory button lead to a better rewards screen giving more control over building synergy, before moving to the next boss. Some options:
Let the player choose a category & then show the 3+skip (4 w/ cornucopia) Add Militia w/ options only from that category
Show a wider selection of Add Militia - say 9 options (3x3 grid) + skip, w/ the middle column showing the icons + description as the normal Add Militia screen, but the two outer columns only showing the icons (mostly just to make it fit on the screen, but also to encourage learning the icons)
An option to remove members from the militia - maybe including duplicates (e.g. sheep or replicating spiders that end up being dissynergistic)
Or maybe just the normal Add Militia screen, but w/ better odds of the rarer levels