For short term, I think these coalitions can work. But there are two problems: First, in a normal big party/small party coalition, the small party typically has a very specific agenda. For example the Green party with environment protection. So it's easy to make a combined program: The program of the big party + that special thing. With two "we do everything" parties, where each party wants to appear as "having made their mark", it's much harder to combine to a big program. And because everybody wants to leave their mark, there is a lot of fighting, so that in the next election, you can rule alone or with a small party, so you'll have more power.

Second: There will always be people not happy with the government. Maybe because they really got handed the short stick, or because they just tend to pick the short stick. That is true even if they are better off than before, just if other people are more better off, people will not be happy. These people want to vote for an opposition. Who should they vote for? They can only go to an extreme party.

> There will always be people not happy with the government.

> Who should they vote for? They can only go to an extreme party.

That is what extremists want you to believe. But the belief that both big parties are corrupt exists in the USA as well, and it helped Trump. The fact of the matter is, if you are unhappy with what a grand coalition does, you can still vote for the party that you agree more with to have it gain more power next time around. Only if you believe that cooperation and compromise themself are bad things, you have to vote extreme.

That is easy to observe in German politics. Yes, some people vote for the party they agree with more, but many do not. This has nothing to do with "the party is corrupt", but with "the party doesn't do what I want them to do".