There is one more idea I want to share.

If there is a bot owner who can produce a viable solution for every possible starting block that fit in say 60 sec threshold and require less than 60 sec for this...  then this botowner is now probably building an alternate blockchain fork from 8000 block. And he will publish this blockchain shortly. His blockchain will be longer than the current blockchain because he can catch it up very quickly. If he can produce a solution in 5 sec then he needs a 5000 * 5 sec ~ 7 hours to produce a chain of 5000 blocks with solutions close to 60secs. Motocoin network will accept his new chain because his chain will be longer than the current one and it is done. This is not a 51% attack this is something different because attacker do not even need a lot of computation power to achieve this.

In other words. A bot owners can produce a blockchain fork as long as they want, each block in the forked chain will contain a solution close to 60sec. Bot owner needs far less time to achieve this than the sum of the thresholds for blocks in the chain itself. An actual block computation complexity is not connected to the threshold itself. This compromise the main idea of a blockchain. A blockchain fork attack complexity is very low now. Motocoin is literally compromised now. I am out.