The entire point of a constitution is to remain unchanged.
The constitution protects people from voting their rights away forever just because they look for a quick solution. This has happened in the past, and to prevent it from happening again, the constitution has been strengthened to the point of banning anticonstitutional parties.
That assumes the constitution isn't tyrannical or hasn't been conceived at a time where everything was different. It's like telling a slave you should follow the law because it's the law.
I don't see how you would look at the German constitution as tyrannical. It guarantees rights, not restrictions. (The German constitution is fairly weak btw, most of its articles are optional.) The only potentially oppressive article is the military draft for men.
What the AfD struggles with is that the constitution enforces democracy. And while this is obviously an instance of the tolerance paradox, prohibiting people from removing democracy is the only way to ensure their rights and freedoms, and most importantly their power to control the government (by voting).
All governments fail their citizens. Nothing is a panacea.
Constitutions exist to provide friction to fast-moving populist votes. They prevent the two wolves from eating mutton after the vote. They are not immutable; they are hard to change, and can limit simple-majority votes.
The constitution protects people from voting their rights away forever just because they look for a quick solution. This has happened in the past, and to prevent it from happening again, the constitution has been strengthened to the point of banning anticonstitutional parties.