Social institutions have changed, but human nature and the soul have not changed. The basic challenges that human beings face have not changed since ancient times. Then and now, people have dealt with inequity, tribalism, injustice, social harmony and disharmony, family challenges, and so forth. The fundamental principles of ethics also have not changed. This is why one can find wisdom and inspiration in literature from a long time ago.
In our era, there are some new "social technologies" to try to grapple with age-old problems - for instance, democracy and the nation-state system - but our challenges as human beings remain the same. Furthermore, all human beings must grapple with mortality, consider what happens after death, and find meaning and purpose in our lives and in the universe. People also often want to know how to improve themselves ethically and spiritually and how to transcend the baser aspects of their existence or avoid being controlled by their lower desires.
Science, technology, access to knowledge, and mass institutionalized education have benefits. However, they do not always make people into kinder or better people. You meet some people who live very simple lives and very little formal education but who have a very good family life and who are generous and treat others well. And, of course, vice versa. In fact, one can say that places which have had the most technological advances and where there is a strong consumerist culture also have more isolation and alienation. So the advances that the modern era has brought to the world are not all things that relate to some of the fundamentals of human existence such as how to coexist with others. Rather, they operate in other areas of life; for instance, curing physical diseases.
So, the challenges of being a human being, and of having a society, are areas where religion provides guidance. Islam, being rather comprehensive, provides a rather lot of guidance on both spiritual and social matters.
As for Islam itself, it is both flexible and inflexible. It is inflexible on some points; for instance, some requirements specified in the Qur'an. At the same time, it has an inherent adaptability to different cultures and situations. Otherwise, it would not have spread to so many different cultures and flourished. We can see in our era that there are various ways Muslims have looked to Islam to solve new problems, whether they be individual or communal. So there is a scope of adaptability that does not confine it to 7th century Arabia and which has allowed it to flourish today, even in places where other organized religions have lost ground.
As for whether society is not as barbaric as it used to be without Islam... looking at the events of the past couple hundred years, such as the trans-Atlantic slave trade, the world wars, crippling economic sanctions, and the deployment of chemical and nuclear weapons... I would not agree with that. There may be more focus in public discourse on individual freedoms, human rights, and the value of a human life, but at the same time there are large masses of people who are dispossessed and suffering due to the current global power structures, and there is more institutionalized inequity than at any other time in the past. Not all lives are treated as having the same worth, as we see in attention given to current conflicts. We also have the capability to do much more horrible things to each other than at any time. So there are some ways that the jahiliyyah Arabian society was barbaric, and there are some ways that the world is barbaric now. In any case, the question of which era is better or worse than another cannot really be answered; just pointing out another side of the question.
So here are a few thoughts. I am sure others will have some excellent insights!