So I think the issue you raised might be fixed by some balancing. In berserk mode, you continuously lose health. Plus the aim is to get as many kills as possible. So the meta should be to switch between the two modes to survive longer and have a chance to get more kills than to just stay in Berserk mode all the time. I believe some additional mechanics/effects can be added to make this more apparent.
But your suggestion is absolutely correct. Thanks for the constructive feedback and taking the time to play my game :)