You are mistaken when thinking that BTC price will drop in proportion to the unbacked Tether used to buy. It will fall MUCH harder than that. The market doesn't move in that way, it isn't money in money out it's about sentiment, liquidity and volume. If the Tether fraud is actually true then BTC is going to go into freefall unfortunately. It is also not possible to accurately predict the bottom. The knock on effect could be catastrophic in the short term as it opens the possibility that any and all crypto coins and tokens are severely manipulated.
Long term it is advantageous because it forces people to look deeply into what they are investing in and do heavy due diligence into everything.