Prime examples of "hard" atheist states would be the Soviet Union, North Korea, and the People's Republic of China and we all know how horrible those shitholes are (or were, in the case of the USSR)
The only real motivation those "hard atheist" states had for persecuting religion was because they saw it as a direct challenge to the dogma they wished to replace it with (namely: Stalinism, Juche, and Maoism, respectively). I really don't think it's accurate to say that a lack of religion was the problem, the real problem was that they were merely replacing one dogma with another far more radical one.
This goes back to what I said a couple of pages ago: it's not religion
specifically that makes a society worse, it's any form of dogma. Once a society is pervaded by an ideology which no one is allowed to question, that society is invariably going to suffer for it.
Even "soft" atheist states that are de jure secular but de facto atheist are usually horrible shitholes as well and tend to be crippled by their own bullshit. Prime examples include Sweden, Germany, and on a regional level, the American West Coast.
I think those societies have their own problems which have nothing to do with religion.
Sweden, for instance, has historically been very isolated, which has encouraged a very altruistic culture among the Swedes. Obviously, this altruism has been misplaced in recent years, but Sweden is still overall a very functional society, and boasts some of the highest reported levels of happiness in the world.
Germany is a country which is still largely reeling from it's history, a fact which has caused them on many occasions to overcorrect, and adopt policies which are clearly imprudent (like allowing the mass migration of culturally dissimilar refugees that obviously weren't properly vetted). Overall though, Germany is really not a bad place to live, and from all of the people I know who've visited, I've heard nothing but good things.
As for California, California's problems are mostly the result of it's high living costs, which are exacerbated by the fact that it has a totally porous border with the other 49 US states, and one of the largest economies in the world. Money being no object though, it's still way better to be in California than the Bible belt. It's not even close.