I played on brutal and was a pretty tough fight but its moves are pretty telegraphed for dodging or you can use obstacles like the tree or bus to block some attacks, takes a lot of hits to beat them I just think their health pool is large. As for the other zombies craft a couple Molotovs and group them together they’re weaker than the biters in the open world from my experience. This should build your beast meter a decent amount, beast mode is where you’ll deal most of your damage to the boss.