It's not a port, and it's a story driven series, so it's very different from something like Minecraft just being ported. It's a new entry in the series, and it looks awful.
Err, it might be easier to just imagine it like Final Fantasy 15 being announced for mobiles?
I haven't had the pleasure of playing the Deus Ex games, but I can understand why you're concerned/annoyed. The fact is though, Square has been on this Doomtrain for a while. Even as far back as FF8, they were releasing mobile games with connectivity to the game... there were items/summons that you couldn't get in FF8 without the Japanese mobile phone game. We never got it, soooo...
Oh, and ever heard of a game called Before Crisis? Another mobile game that was never released in the US-- from the FF7 franchise! A lot of people are really irritated that we never got ANY playable version of it (though it's actually supposed to be quite good, to SE's credit).
There are some quality mobile titles out there, though stinkers like All The Bravest certainly do not inspire confidence. Hopefully this will prove to be a solid experience.
Also, don't mind the rate-downs. There are people here who think you make fair points and understand your need to rant about your concerns, and there are other people that will take any amount of skepticism towards SE as if you personally pissed in their Cheerios. Personally I don't support the way you've been made into a whipping boy just for not having faith in SE (when not long ago, ain't NOBODY had faith in SE). It's just tribalism and console wars and fanboyism in general. And all the cool kids don't filter sub-default posts anyway.
Don't sweat it.