1. As far as I know, mining has a diff (difficulty), meaning that as the hashrate increases, the diff also increases. So, does the increasing of the hashrate make it harder to hit the jackpot in Bitcoin mining? Or conversely, does the decreasing of the hashrate increase the chances?
Yes and yes.
2. Are you referring to solo mining ? If so, can we increase our chances by purchasing more of these mining devices? Is that like buying more lottery tickets?
Yes and yes. However, consider that most Bitaxes are mining on a mining pool like CKPool. That is not exactly "solo", but the specific pool rewards you 98% of the block reward if you solve it. You do have to trust it, though. You can setup your own CKPool instance, even though I wouldn't recommend it to the fullest unless you know what you're doing. (It'd be a pity if you solved a block, but your node couldn't broadcast it successfully, for example.)
3. If the chance of a miracle in Bitcoin (the mining) is greater, then shouldn't we choose to mine as you are referring to, rather than buying lottery tickets? and that is what you are implying, right?
I know. I agree.
