Whether this card is efficient or not will depend if they targeted the sweet spot or just went for raw performance. Vega 56 and 64 could get could power efficiency when undervolted, they were just pushed too hard out of the factory.
She talked about 25 percent more performance for the same power draw yet again, as was emphasised last year when the first 7nm parts were confirmed. Well, this card is something like 25-30 percent faster than a Vega 64.
So it's likely to still be rather power hungry unless AMD have managed to do a lot of work on the power profile side of the GPU.
Hopefully it's less than a Vega 64 but it needs to be quite a lot less. RTX2080 is only 225w under max gaming load. 250w would at least make people more interested when in a head to head against the RTX2080. 300w will put them off like it did for the Vega 64.
I do not think you are well learned on Vega 56 & 64.
As other have attempted to convey with you is that Vega's design IS very efficient when not pushed to it's limits (as AMD had to do, when releasing Vega, because they had to met a certain price/performance ratio.)
But if you ran Vega slightly underclocked, it's efficiency rose considerably. And you didn't lose much performance, or low frames times, because the card ran so much cooler, that it didn't throttle all the time, of have heat soak, etc.
Now, if you start out with 1.8GHz chips and you are not overvolting them (like they did with the 1.4Ghz 1st gen), then you will not have the excessive power draw you had on Stock Vega's a year ago.
Secondly, if you are going from 14nm to 7nm you can be conservative and EASILY understand that Radeon 7 (VEGA2) is not going to hotbox People's systems.