When the iMac Pro was released in 2017 it was the first generation Xeon-W (21xx) and used the latest C422 chipset. The second Gen Xeon-W (22xx) suitable as a replacement was introduced in Q4 of 2019, which was around the same timeframe as the 2019 Mac Pro (Xeon-W 32xx) series was introduced. By that time, the iMac Pro had served its purpose as an interim gap between the 2013 and 2019 Mac Pro. At no time during the two years before the 2019 Mac Pro was introduced was the 2017 iMac Pro out of date or had “dated internals that were a couple of generations old.”Apple doesn't sell the iMac Pro anymore, and even when they did its internals were a couple of generations out of date. Apple Silicon doesn't need this kind of cherry-picked stat in order to justify its existence.
The 2017 iMac Pro is an excellent choice for a comparison as the 10-core has the highest single-core score, scores well in multi-core and was a cheap upgrade for those that took the iMac Pro plunge. Users who bought an iMac Pro are about at the point where they are looking for a replacement and this stat will be relevant to them.