None of these three will be the nominee, but good news for Brown nonetheless.
What makes you say that? I doubt Blackwell runs, let alone wins the primary if he does. But I can't fathom how either Taylor or Mandel doesn't otherwise wind up nominated. Jim Jordan could excite the ultra-right, but I don't think he's running either. Taylor and Mandel both have strong party backing which counts A LOT in the OH GOP.
The big question is whether a deal can be worked out to avoid a primary, as is the OH GOP's forte. If not, the secondary question is whether a prominent ultra-conservative like Blackwell or Jordan will jump into the fray and try to squeeze out a win by getting True Believers to put him over the top in a 3 way race.
With respect, the OH GOP isn't prone to nominating "grass roots challengers" or sacrificial lambs in any race that is even remotely competitive.