Power certainly exists, its just less popular. The above board is under $250 and seems to be good enough for tinkering usage.
Software support is certainly weaker. I think Power9 primarily exists for people who are planning to write their own application servers, or otherwise are willing to spend time recompiling OSS over to the Power9 architecture (Gentoo style or similar).
A "real" server application will want to buy a Talos II Workstation, for $3000+. If you're worried about performance, you have to develop and test on the big stuff.
If you're planning on a high-performance database optimizations (ie: lets say you wanted to improve PostgreSQL's performance), you wouldn't test on a Rasp. Pi or Intel i7. You'd buy a Thunderx2 ARM, Intel Gold, or AMD EPYC to test on. The architecture of "big boy" chips is grossly different than the smaller scale stuff.
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And the way you "test" on big-boy machines, is through cloud services. You don't necessarily have to buy a full machine if you're testing (although local access is certainly useful).