I'm playing my first Diety game as Gorgo right now and it's a cake walk thus far. I'm going for a domination win. My strategy is simple: I'll build no more than 3 cities (including capital) with settlers and plan to conquer the rest. My cities are building nothing but military units, builders as needed, trade units when needed, and 4 districts exclusively in this order of importance: commercial, industrial, encampment, and harbors. My builders focus on building mines and improving resources. New cities get a bunch of trade routes and builders to help get them off the ground as needed. I make exceptions where needed but basically I'm going full throttle on the conquest and trying to keep my cities growing as slow as possible to up production.
What I'm not doing is building campuses, wonders, great people, or theatres. I'll might build an entertainment complex eventually but haven't had the need to yet. Despite this I'm able to keep up in the tech and civics trees (mostly by leveraging inspirations and eureka) thus far. Amenities aren't proving a problem either (when they do, I plan to raze cities) as I'm avoiding housing to keep populations low, I tend to get new amenities every few cities I conquer, and I'm not shy about razing cities.
Anyway, I bring this up to point out that on Diety level I'm having a rather easy time of it focusing exclusively on production and conquest. I'm ignoring half of the game mechanics and actively trying to keep my cities small and it appears to only be to my benefit. Granted, I'm only in the late middle ages but I cannot believe how little of a struggle I'm having using this strategy when in past Civ games I'd be fretting about my tech or having too many cities by this time. Also, from experience I realize that, if I pushed to go tall, I'd likely have fewer cities and be struggling at this point.
This to me tells me tall might be dead. It might technically be viable in that you can win the game with 4 to 6 cities and the right strategy on Diety. But going wide with small cities just seems to make everything so much easier and looking at the game mechanics, it isn't hard to see why.