Would re-importing reduce the DB/backup size?
Short answer:  It depends.

Long answer:

It depends on what Engine you are using.

It depends on the value of innodb_file_per_table when you created the tables.

It depends on whether you have inserted about as many rows as you have deleted.

It depends on what you mean by "changelog".

It depends on what you do to clear the disk space between the dump and the reload.

But most likely the answer is:  The disk footprint won't shrink any, or at least not much.

YMMV -- Try it.