Commenting only on the last paragraph, existing decision theory addresses this adequately: if only a big win is acceptable and everything lesser is essentially equivalent, then according to pretty much any decision theory, you should maximize your probability of achieving that big win even when probability is small.
Kelly betting maximizes long-run expected growth rate, but not probability of reaching a threshold. The criteria for maximizing chance to reach a (large) target are more complex depending upon the context, but are generally less conservative.
Commenting only on the last paragraph, existing decision theory addresses this adequately: if only a big win is acceptable and everything lesser is essentially equivalent, then according to pretty much any decision theory, you should maximize your probability of achieving that big win even when probability is small.
Kelly betting maximizes long-run expected growth rate, but not probability of reaching a threshold. The criteria for maximizing chance to reach a (large) target are more complex depending upon the context, but are generally less conservative.