What are you inferring they are saying? If you're saying they don't accept Bahaullah as of yet you're right but the world is fully accepting Baha'u'llah's principles and teachings.
All of them? Surely not. For example polytheists disagree on how many gods there are and atheists, agnostics and most Buddhists do not accept the existence of God. Christians do not accept the principle of continuing emanating and Jews and Muslims consider prophets to be simple humans whom God has favored, nothing else. What is the agreement about? Now do not say world peace! Everyone desires peace before something else takes greater precedence.
Atheists and humanists would say abandoning religion and using logic and empericism as the guide to life will create world peace.
Jainas would say following their dictum of strict non violence and pluralism regarding truth will create world peace.
Buddhists would say the same. They may point to Asoka. SoKaGaKa will go further.
Amish and Quakers would say their way of practicing Christianity, if followed by all will create world peace.
Any Gandhian and would point to undoubted success of ahimsa and satyagraha as tried and true ways to promote peace. Who can deny its impact in India, US, South Africa and now in Myanmar?
I am happy to see that Bahai seek peace and harmony and prioritize it. But what is it that you have that other ideologies I mention do not that supports your claim that only the Bahai can deliver world peace and all of us should acknowledge the primacy of your teachings over others? I do not see anything special here that holds my attention. I mean if everybody followed the Golden rule at all times even then there would be world peace. I can start a follow the golden rule drive and proselytize on that alone correctly claiming, if successful, there would create world peace. So what's so special about your beliefs that would make it the only one that can usher world peace?