maybe it screws roi in terms of btc.
but maybe it keeps btc price higher in terms of usd. (pick any currency)
Lower difficulty=more BTC for us=maybe same money with a lower exchange rate. Talking about the "what if" is hard especially when there is nothing to do right now. The reality is that they increased the hashrate for everyone.
You should take note that Bitfury uses customer funds to build mega farms and screw their customers ROI.
What difference do you think that actually makes? Whether they mine with their own systems or sell them to customers, the same amount of hashing power is still being added to the network so customers ROI will be the exact same.
They deploy hashrate at cost. Selling it to customers for a mark-up would mean that less hashrate is added for the same because of the cost difference and maybe because other unknown reasons.