What evidence do you have that failure to provide lifetime tenure to non-performing rabbonim in chinuch will jeopardize the future supply of rabbonim willing to pursue a career in chinuch.
What evidence do you have that underperforming rebbeim have a negative affect on children?
Same as I have. Common sense.
right now, there are too many rabbonim coming out of yeshivot who surpress the salary of teachers
Higher salaries mean higher tuition, and the tuition burden is already crushing many middle class families.
The issue the OP presents (which is a serious one) is not that underqualified people are going into chinuch, it’s that they get burnt out. Within the first few years of a rebbe’s career, it’s not such a dilemma to fire them.
Raising salaries won’t solve this.