HTB has described to a tee most every baptistic church with which I have ever fellowshipped. The SBC, for just one example, is an association. It’s not a controlling hierarchy. Individual pastorates are filled by deliberation of the local body of believers. Indeed, these congregations do tend tob retain their conservatism despite failures of association leadership.
The main threat of corruption, IMHO, in these scenarios is the association seminaries. If they go bad, then it becomes more difficult to find good pastoral leadership. This is essentially what happened to American Presbyterianism early last century. The modernists staged a coup in the seminaries, took the money, the property, and effectively forced those who wanted to remain conservative to flee and form new churches.