I would think the occasional unicorn would be more prevalent amongst a sea of small successes than just randomly, but not sure if anyone’s done the math in this
I actually doubt it. The strategy for building and releasing a successful screen recorder app or affiliate system (two of OP's businesses) is dramatically different from the strategy for launching a unicorn, starting with the problem you decide to solve.
When you're trying to launch a small success you pick a niche that is small enough that no one is competing there yet, then build for it while keeping your costs as low as possible. There's basically zero chance of that turning into a unicorn because you picked the wrong market and aren't investing enough money in it, but there's a relatively high chance that you'll get enough customers for a modest exit or lifestyle business.
A startup with a chance at becoming a unicorn needs to pick a market that is big enough to support a unicorn, which are exactly the markets to avoid if you're trying to start a small success. Then you have to execute completely differently, spending tons of money long before profit materializes in the hope that you'll build something awesome before you run out. If you try to take it slowly and are in a good market you'll be passed up by someone who ran.