Which, as we speak, are really high. Most recent block - 817080 - was mined with 193 sat/vb median fee (!), gathering a total of 2.1 BTC (!!!) from transaction fees alone.

Their reasoning goes as following: whether we rise the block size or not, there will still be scalability problem. Even if the block size limit was 1 GB, the spam attack would cost nearly zero, and there would probably still exist a fee market (much less intensive than now of course). People would really take advantage of the 144 gigabytes of space every day. You can verify that on BSV blockchain, where they have saved whole movies. Needless to say that with 1 GB of block space, one mining pool can take advantage of the time it takes to verify the block and kill off the competition.

This is an indication that we need more than just one layer.