Siacoin growth is shrinking. this happens as we see it today.
yes agree with you. When i first bought sia its supply was near 22b and price @ 414 Sat and i have lost it all... some because of BTC price and also due to its supply which is over 30b now and counting. 
Sia use is growing and growing ... Dont set in your mind that the Sat price is the companys use graph !
Here are the October News of Sia Team
https://blog.sia.tech/sia-community-update-october-ecf673f41e96
TAKE A LOOK AT THE Use Graph Size of total Contracts in the SIA Network ...
So I really think SIA is growing very well ....