Right now, to get the count of element from bynder we need to retrieve all the assets and count them because the used SDK does not provide another way. But the API has a count end point:

https://bynder.docs.apiary.io/#reference/assets/asset-operations/retrieve-assets
count
 
Indicating whether or not the response should include count results. This parameter when passed as 1 overrides the total parameter.
 Example: 1. Default: 0.