So it took me about 4-5 attempts to get to 300+ after reading people's advice to stay in the corner. First run, gunners came in later but the later runs they seem to spawn so early which chunked me before I could really make anything. It's RNG i'd say if you play it normally by running around which can make for a frustrating experience. Aside from that, I see a lot of potential from this game and it's atmosphere. Love Nakano's character too. Looking forward to your updates dev!
For those having trouble, I also noted slowly clicking over enemies will make it easier for your horde to surround them and kill them faster. If gunners shoot at you in the corner try not to interact with them and they'll wander off hopefully, otherwise fight them if they are a smaller group and don't revive them.