I agree with your estimation, regarding the CL reward set. However, there's also some DEC minted from the CL core set cards and it could increase in the future. I have burned some of them in the past. I currently own about 900k DEC in cards to be burned. Most of them are in the rental market. I will eventually burn them if I am unable to sell them, likely before the Conclave Arcana pre-sale.
Without Survival mode, the number of cards to be burned would be even higher. With that said, we still have to see how it performs and how the market reacts to it and to CL rotating out of Modern.
There's also some DEC minting risk from burning SoulKeep assets.