You may easily manually check. Using average as integer when it comes to pretty same NOTES will round the result. You get much more accurate average value if you will use 2 decimals instead.
See this:
Using LocalDB as source of DVL - Thunkable Discuss - Community
and you will see that I’m complaining about the speed when using local tables too. For Airtable, GoogleSheets is even worst when it comes to do calculations with large data…
@domhnallohanlon promised me that will provide an answer so I’m confident 
Maybe in your case you can implement some trick that @muneer taught us, about making another filtered sheets from original sheets in Airtable, then use that for DVL. This way you can sum directly an entire column from filtered and speed up the app.