It’s just that things like the Zuflussprinzip don’t seem to work as they are intended to and because you are dealing with a bureaucratic institution. It feels that these rule-made principles are prone to misuse or abuse.
ALG1 is based on your income over the past 12 months. It’s 60% of the monthly average.
ALG2 is based on your living expenses. It covers your rent plus 450-500€ depending on the number of dependants.
There are also some other benefits that one can apply for regardless of employment status, e.g. Household benefits (Wohngeld), which aims to help with covering rent with ~200€. Being eligible for these obv. requires being below a certain income threshold.
My expenses (rent, utilities and food) were pretty much covered. Obviously it wouldn’t cover a certain lifestyle, but I’m generally frugal, so I didn’t notice a difference.