No one uses 1080 Ti for ETH mining, that's not what these cards excel at. It's just ETH is the largest alt coin, and because of that it became some kind of universal "mining benchmark" (mostly for sites/channels where people know very little about mining). Nvidia cards with gddr5x memory (gtx 1080, 1080 ti, titan xp) are not competitive in ETH mining, they're good with other algos, so when you try to figure out profitability you don't compare something like 295x2 mining ETH to gtx 1080 ti mining ETH, you compare it to 1080 ti mining whatever it is the most profitable for nvidia cards at the moment. Which might be equihash, or Lyra2REv2, or skunkhash, or a dozen other algos.

And I'm not even sure that ETH is the most profitable algo for 295x2 cards, right now they're probably doing better on cryptonight.