Based on what? a 12tf gpu does not perform identically to a 10tf GPU
CPU is faster on X, but thats close to a wash
Then you have the faster ram
Ps5 has the faster SSD
The performance will not be identical.
There are other non-trivial differences that will require more devs input to explain:
The PS5 have a cache-scrubbing engine which prevents costly GPU stalls when streaming data while rendering.
The XSX have sample feedback which might allow more granular texture streaming, and compensate some streaming speed differences.
Differences in the CPU architecture, both Sony and MS might have asked modifications to Zen2, and that can go either way.
Cache architecture and amount are is still unknown for both.
Cerny said narrow/fast is better than wide/slow for the same ALU grunt available. We have no metrics for specific cases about this.
Audio engine is different, PS5 uses a general purpose cell-like architecture, XSX is more DSP-like from their description. It might impact memory hits and streaming priority hits differently. And the PS5 side can help reduce CPU usage if it can be used for other tasks.
The additional I/O co-processors are quite different between the two, and they will affect CPU usage differently.
Regardless of specs, some important differences might appear in third parties because of the ease of development, or profiling tools, or more low-level access.
Considering the cost of RT even with very low resolution buffers, XSX/XSS devs having to target a 4TF console from the same executable might impact development choices between RT and baking, which would be a different decision on PS5, specially on first parties.