This is misinformation and you are confusing people.

That number isn't true as it assumes we will immediately be processing 84k transactions per block which isn't going to happen.
20GB is the future limit and not the size of most blocks in the future. We are only 600-700tpb at the moment
https://blockchain.info/charts/n-transactions-per-block which means we are typically 15-25% full blocks for 1MB blocks.... do you really expect this to shoot up to 100% full 20MB blocks overnight?.... it will take years to start getting close to those levels.

Additionally, you are completed ignoring the work that is being completed on merkle tree pruning.

P.S... You may ask yourself why bother if we aren't even fully utilizing 1MB blocks now ... the answer is that we are having more and more examples where the 1 MB block limit is preventing more transactions from confirming and this is only going to get worse with each passing day.

Analogy to think about --- Why do gamers look for gfx cards that can support incredibly high fps rendering their games avg's of 120fps when their monitors typically won't reflect more than 60 fps and they would be hard pressed to tell much of a difference between 30 to 60 fps with their naked eye? Answer- because avg fps doesn't matter but minimum fps matters and if you buy a gfx card that benchmarks 1080p @ 50fps , it may occasionally dip to 10-18fps during certain moments of the game and create major moments of lag.