What you are saying still make no Sense, and reality dont bend to fit what you want.
You are still buying steem with BTC. So the steem/usd still derive from BTC/usd pair.
You cant accurately evaluate the usd price of something If this something is not directly traded for usd.
Any price movements that happen on steem/usd is heavily affected by the price of BTC/usd.
The price increase because the BTC price increased. Check the graph below from Tradingview that show the % price change from these 3 pair:
Since It started Trading on bittrex, steem Lost 64% of its price, while Bitcoin increased 2300% of the price.
Now Tell me, what made the steem/usd price rise? If you didnt Saw It yet i Will Tell you: BTC is what drive steem/usd price up.
All movements of steem/usd price ia a reflectir of BTC/usd graph.