They aren't the best, they are different, and the best in certain areas. In terms of cache size they are way out in front. That architecture has very very fat cores. That's the main thing that makes them different (not better or worse) than something like x86_64, is the focus on single thread performance and cache rather than more cores. If you have a transaction processing app that you can't shard and that scales mostly with single thread perf, then they are pretty well suited for that use case.
I'm speaking more to the marketing checklist sense, IBM wants features that the others don't quite have yet. This is luxury branding imo a great degree, customers are paying a lot for a super-premium product, so they need to think they are getting 'the best'.
In terms of actual functionality, no matter how good it is, its not price-competitive.
