You won't need it to burn 300W if they want just 30% improvement like
@SmokSmog calculates.
Raptor Cove is going to end up being few % faster per clock. Simply lowering the clock(and voltage a bit too) to make it equal to Golden Cove will free up quite a bit of TDP for the extra E cores.
Also assumes there will be zero which makes little sense as refreshes get 100-200MHz at same TDP. 1185G7 to 1195G7 is 3.4% increase in base clocks and 4.2% increase in max Turbo. If you get few % of efficiency on the Gracemont portion, again they can keep the clocks same to reduce the power per core a bit too.
You can see here the 8+0 with no power limit is just 10% faster in average MT applications compared to 125W limited 8+0.
Intel Alder Lake im Test: Leistung und Effizienz P- vs. E-Core / Wie effizient ist die Hybrid-Architektur?
www.computerbase.de
However, Intel doesn't need to cut P core power by half to 125W.
In fact it shows that 8+0 can use nearly 250W by itself! That's why with extra E cores it's worth it to back down the P cores slightly and get massive boost in MT performance at the same TDP. Alderlake has to max the P cores to squeeze the last few % of performance. Raptorlake will be comparably much more efficient even if nothing gets better because of this.
There were some rumors that Alderlake was to be mobile only. Clearly you can see how much they have to push 8+8. 8+16 will be far better.