WU Bubble vs Airtable db

I’m trying to understand if there’s a difference in WU load when using Bubble’s database vs Airtable via API.

I like using Airtable because it’s quick to build the backend. But I notice data loads slower in my app, because it’s doing an external API call. I’ve recently migrated one of my tables to Bubble’s database, flipped over the data source on pages, and it’s significantly faster.

Is there a difference in WU, even though the page queries and structure is the same? Does Bubble “charge” more for an external API call vs internal query?