Does Google Drive sync entire file again on making small changes?

The feature you are asking is called "Block-Level File Copying". With this feature, when you make a change to a file, rather than copying the entire file from your hard drive to the cloud server again, only the parts of the file that changed (called the delta) get sent.

A Google Drive sync cannot be partial. If a small change is made to a large file, it redoes the entire file rather than just the change. Google Drive isn’t capable of doing block-level file copies.

As far as I know, among the best-known cloud providers, only Dropbox has this feature for all file types. Dropbox partitions every single file it stores into 4MB blocks. Each block is hashed with SHA-256 and a list of these hashes gets stored in what’s called a “blocklist” for reference.

This feature is also shared by OneDrive, which however only supports it for Microsoft Office documents.

For more information and some benchmarks, see the article
Block-Level File Copying and the Cloud.