Can Alderlake 8+8 be competitive?
Well let's see.
This is assuming all 16 cores can work in tandem, Gracemont cores included.
In the U form factor, if you take my simple calculations above, 8 Gracemont cores should get 1600 in Cinebench R20. Perhaps with even higher TDP it can clock 10-15% higher.
1800 for 8 Gracemont
10 Skylake cores get 6300 in R20. Moving to 8 Willow Cove cores, the improved uarch cancels out the 2 extra cores. Assuming 20% further gain from Golden Cove, we get -
7600 for 8 Golden Cove
If you simply add the two, you get ~9400, which is on par with the Ryzen 9 3950X. By that metric it can get quite close. It does need few addendums though.
-If Hyperthreading can be active for Golden Cove for a total of 24 threads. On Lakefield, Sunny Cove's HT is inactive.
-If having two sets of cores work together does not create any contention.*
-If applications/OS support is good enough that combined performance is representative of performance for vast majority of applications.
*Cinebench could be close to the ideal case because it can simply be made to split up workloads into 24 sections. Not all threaded applications are going to be like this.
One could think of the hybrid state as "Hyperthreading 2.0". Where potential gains in perf/watt is there but with further complications in coding and support.