This seems fun! I can imagine trying to kill zombies faster so the boss shows up, you have more aggro than the opponent, the boss comes towards you... I wonder how easily can you break this, if you might easily end the game with every miniature with about 100 aggro.... If you can build an engine of 3+ rifles you can really create a meat grinder.

I feel you took more or less my path of design, instead of lowering the amount of elements, you increased the amount of stuff that happens for each element.

I always love a good game that involves AI monsters. Seems like a lot of people did something similar! Lots of Hunt:Showdown inspiration! 

• "Sweat" is a good term.  Having zombies show up anywhere is fine, though in practice it usually meant "put them very close to the enemy player" which wound up making LOTS of chaff for the player to cut through. Loads of zombie minis, for sure! Is there a way to get rid of sweat?
• Aggro staying around is a bit tricky; a quick playtest had me ending up with a lot of tokens. Not a deal-breaker of course.
• Some proofreading would be good; under "reinforcements" for example, you have "If a ___ has lost a model" 
  
• The 6x4 board ended up feeling a bit large and maybe wasteful. Lots of space simply wasn't used. It was a bit odd that the first thing the boss did was leave the central area, exiting the protective presence of a cluster of mobs. Seemed easy to kite.
• Those points of interest are a pretty hard sell, since the benefits seem pretty small and the dangers are high. But I guess it's also something you can use offensively during placement.
• The dual purpose design is the sweat generation, I think?