#Vendor/Part per buyer

Hi Community I am working in manufacturing company located in 2 production site as supervisor. Since 7 years we have growth double % each year, our raw materiel purchased spend increase 40% with over this period about 3000 parts to manage. We do not have strategic department managing our contract. Each buyer manage replenishment- negotiation , shortage... With 3000 parts to manage we are only 4 buyers. We dropped all strategic tasks and focus on replenishment only, each buyer have about 750 parts to manage. Am i the only thinking this is too much. I know this is tough to compare but how many part/ vendor are you managing or your team managing. I just want to know if this is our productivity the issue or the human ressources. Thank you for your input