All valid points.
But throughput per socket is also a major consideration because it's not just the chip but the surrounding system that costs money. The rest of the system ain't cheap, and the less cheap the rest of the system is, the more value Graviton2 loses. So while Graviton2 might look like a good value, if total system cost for TWO graviton systems exceeds the cost of ONE 7742, then it is not a winning proposition globally.
As a key point, the reference Daytona rack that is 2 x 7742 costs $25,000, of which about $14,000 is the 2x7742. So... the systems ain't cheap ($11,000 for the surrounding system).
Imagine a 2 x Graviton2, even if the chips cost $2,000 each, which would be a good bargain, a similar system would cost $15,000.
2P implementation comparison
2 x Graviton -- $15,000 -- 100% speed
2 x 7742 -- $25,000 -- 250% speed
Or if you want to try to equal the 2 x 7742
4 x Graviton -- $30,000 -- 200% speed
2 x 7742 -- $25,000 -- 250% speed
Unless they're selling Graviton2 for like... well, they could give it away, and the 4 x implementation would still be barely be cheaper than the 2 x 7742 that is faster. And 4 x Graviton (2 x 2P systems) will not have the energy efficiency benefit over a 2 x 7742 (1 x 2P system) that Amazon are claiming for the chip alone.
How many years will Graviton2 take to make up the speed deficit with its cost-efficiency? Until we know pricing and implementation, that's hard to say. And I'm not sure the profit Amazon make on the contracts to lease out the instances (in other words, profit per instance and # of instances per thread per day), which is also a consideration.
