You’re looking backwards not forwards. Assuming transaction fees of 1BTC / block, the next drop isn’t to 3.125 BTC it’s ~4.125 BTC and the drop after that is to 2.5625 not 1.5625. In roughly 3 drops subsidies will be less than block fees.

Not that 1BTC per transaction is anything close to a constant, maximum rewards over the last 3 years where more than 100x minimum rewards, but it does seem independent of block rewards.