I suggest you to use bulk api endpoints, for better performance.
Tier price updates the endpoint is
{{host}}/rest/async/bulk/V1/products/tier-prices/
or
{{host}}/rest/all/async/bulk/V1/products/tier-prices/
or
{{host}}/rest/<storecode>/async/bulk/V1/products/tier-prices/
Here an example of the json payload
[{
"prices": [
{
"price": 66,
"price_type": "fixed",
"website_id": 0,
"sku": "juice-lemon",
"customer_group": "Gold",
"quantity": 1
},
{
"price": 55,
"price_type": "fixed",
"website_id": 0,
"sku": "juice-lemon",
"customer_group": "Silver",
"quantity": 1
},
{
"price": 44,
"price_type": "fixed",
"website_id": 0,
"sku": "juice-orange",
"customer_group": "Black",
"quantity": 1
},
]
}
]
You can find format and fields explanation at the tier-price REST official documentaion
https://devdocs.magento.com/guides/v2.4/rest/modules/catalog-pricing.html#manage-tier-prices
Here is the documentation about bulk endpoints and how they work
https://devdocs.magento.com/guides/v2.4/rest/bulk-endpoints.html