I agree that sharding/scaling is definitely a problem, but I'm not sure where you got your numbers from. I don't know about Stellar, but for Ethereum a full sync takes 16 hours to a day for me (which I find slow, but it's certainly not a week). And that full sync results in about 125-150 GB of disk usage. Again, I personally still find that quite much, but it's definitely not "well over a TB".