Wouldn't they still have to deal with filibusters?
They ran through several rounds where they couldn't even pick a house majority leader among their own party.
The tariffs would be very difficult considering each of their local concerns.
See https://en.wikipedia.org/wiki/German_balanced_budget_amendme...
The American debt limit regularly shuts down the government, but debt still keeps piling up. The German debt brake doesn't seem to shut down the government, but actually lead to a substantial drop in the debt-to-gdp ratio.