I really don't know how you decide that.
I didn't decide it. People did. I challenge you to find a poll, list or group of people who would agree with you that David and Joshua are more important than Jesus or Mohammad in terms of religious influence upon our modern world.
Without Joshua there is no story to continue
Without David there is no story to continue
Every character in a story is necessary for the story to continue. That doesn't mean that some characters aren't "more important" or "significant" than others.
For example, who is more important in the play "Romeo and Juliet", Romeo or Mercutio? Mercutio influences the course of the play and has lines that add to the story, but he is not the "most important" or "significant" figure in the play.
Jesus > David > Joshua in terms of significance.
And one way or another you've got to deal with the fact that the bible attributes their attrocities to the command of the God we see in Jesus.
Yup, it was a barbaric, tribal culture. You also realize that Islam places high importance on the Jewish scriptures as well, right? They follow David's name with a "pbuh" because they regard him as a prophet.
So, both Islam and Christianity share those barbaric, tribal bits of the Bible together.
Then, both Islam and Christianity
expanded upon those Jewish scriptures. Christianity expanded upon it with what appears to be somewhat of a moral evolution with Pauline Christianity spreading via testimony, witness, healings, helping the poor, etc. Mohammad's Islam expanded upon it with what appears to be essentially identical moral status: spreading by war and violence.
BTW, I think Paul and Mohammad have a more analogous relationship to their religions than comparing Jesus and Mohammad.
You tried to imply that Mohammed's wars were spectacularly horrific.
the reality is they were not. They were quite a bit less horrific than a lot of other similar wars and massively less horrific than the wars our culture has perpetuated, often with full support of christians.
If you want to see his compassion I suggest you read the Quran, reflectively and with charity, preferably in a good modern translation like Haleem's
If a man in one breath writes about compassion and in the next raises an army which kills thousands, it somewhat cheapens his writings, don't you think? He does indeed say good things in the Quran, but, when push comes to shove, a Muslim has two options: violence or non-violence. I think it is
easier to justify violence in Islam than in other major religions. This is evidenced by Islamic fundamentalism which is generally characterized by violence.