There is another problem that makes the downloads so big: Every day large 'updates' are being downloaded. You can easily test that. Make sure your client is up to date. Then disconnect them from the proxy (eg pull out network cable). Wait 1 day. Open the Eset client and get ready to force refreshing the updates. Start making a screen video, put the network cable back in and hit the refresh update button.
You will notice the first a small download is fetched, which is normal after 12 hours (a level 3 update). But immediately after that a very large download comes in (a Level 1 download). You might say this can happen, bit this happens every single day.
ESET needs to fix this urgently, because their small updates was one of the last USP. I would hate to loose that.