Zen 2 or Skylake, total nonsense. You bought the marketing. Anandtech tested E core performance exhaustively. The 12900K has 8 E cores and it often loses to 4 Skylake cores. So half the speed of Skylake or Zen 2 is more like it.
"Having a full eight E-cores compared to Skylake's 4C/8T arrangement helps in a lot of scenarios that are compute limited. When we move to more memory limited environments, or with cross-talk, then the E-cores are a bit more limited due to the cache structure and the long core-to-core latencies."
The issue is one single E core can appear to equal a Skylake core, all by itself. But when you run 8 of them together, the core performance doesn't scale right because of their limited design. Look at the MT tests and you'll get almost half the performance as what you expected.
E cores are small for a reason. Lacking cache, high latency, lacking hyper threading, don't expect much from 16 of them. CPUs are more than the raw compute core. I don't want any E cores at all, thank you.
CPU Benchmark Performance: E-Core - The Intel 12th Gen Core i9-12900K Review: Hybrid Performance Brings Hybrid Complexity (anandtech.com)