I would refer you to an article by Church of Christ, John William McGarvey, “Missionary Societies” (1868), in which he argues that missionary societies are a modern invention which is unbiblical.
I think the issue here is very well put by McGarvey, when he argues that we are not at liberty to “invent” new conventions, organizations, and methods (especially not changing the content of the gospel message).
He argues that it is legitimate to use the means available (which best accomplish our biblically set goals), but not parting from the methodology and precedent set in the Bible.
Here the issue would come down to the following conclusion…
We “NEED” mission boards because local churches refuse to obey Scriptures and be the sending organization that equally supports with actual follow-up of activities, money, time, personnel, etc. to complete the mission God gave us. Instead of doing the job God gave them to do, local churches have abandoned this to unbilical third parties (i.e. mission organizations) which have no scriptural warrant, and which today have taken over missions. While they divert millions of dollars into US stateside buildings and self promotions, they drain away precious scarce mission resources, personnel, and dollars into”non-missions” ministries, i.e. activities which drain but do not directly get people saved, which do not directly disciple people in a local church.
Today the majority of the money which is given in local churches to “missions” does not comply with fulfilling the great commission, i.e. it does not pay the salary of an individual that goes into another country to win the lost, nor to plant and raise up local churches. This is the great higher and better vision of mission boards than local churches.
To be involved in missions and to live from missions, every missions minister should be witnessing weekly in the street. To accept anything less is sheer hypocripsy. Why is it acceptable for a mission’s board director and office staff NOT WITNESS WEEKLY yet they demand their missionaries to do it? Isn’t hypocripsy holding (and beating others with the thing) a higher standard for others, yet accept a lower standard for one’s own self?