If we can mine with pre-computed data, that is, the data is the mining machine, then even if the block reward decreases or the coin price decreases, it will not cause the hash rate to drop significantly. Because the cost of storing this data is very low.
I do not understand this or your proposal does not make sense.
Pre-computed data is just block hashes, mining is the process of scanning for a random block hash under a particular threshold. How do you take things that are already known, and turn them into something random?
Things that are random and have a sufficiently large range also naturally use more time to solve, because (again) the range is what makes mining so intensive, and expensive.