Do you mean because of the information leaked when going from taddr → zaddr? I agree that if in the whole world only me with my eg 5ZEC has ever transfered money to a zaddr, then if there is a txn from zaddr → zaddr, people can guess that it’s me and guess that it’s <5ZEC, but zero-knowledge is zero-knowledge 
Also the link you gave – 2989/(2989+52,852+311,964) = ~0.008126588 => ~0.8% of ZEC currently stored in shielded addresses, I’ve been keeping an eye on that and you were probably off by an order of magnitude, it was 0.5% until recently so it is actually growing!