You realise that about 95% of Mark is also in Matthew.
This isn't strictly true. Only some of what is common to both is identical in wording. The rest has significant differences in wording and detail. For example, compare Mat 15:16 with Mark 7:19.
Mark says, "‘So also ye are without understanding! Do ye not perceive that nothing from without entering into the man is able to defile him? 19because it does not enter into his heart, but into the belly...."
whereas Matthew just says, "Are ye also yet without understanding? 17do ye not understand that all that is going into the mouth doth pass into the belly".
Although they are both clear, Mark's is easier to understand because he adds that food doesn't go into the heart.
If Mark's criteria for dropping things included "it's already in Matthew", he would not have written a gospel at all.
Unless he had more detail to add or felt he could make some bits easier to understand.
Jairus' name is a pretty inconsequential detail. The Lord's Prayer is fundamental.
Assuming Mark did write Mark: his mother's house was a meeting place for the early church, so they would have known about Jesus' birth, what he said in his sermons and whom Jesus had appeared to after the resurrection. If he wrote the first gospel account, why did he omit these details - assuming he knew them? Isn't it more likely that they had already been written down (so were available for Christians to read), and were not important for the purpose of his book?