You are right that every TM can be converted into a Collatz-like problem using Conway's Fractran compilation. So technically the statement "Solving the BB(n, k) problem is at least as hard as solving a Collatz-like problem." is true in general.
However, the Collatz-like problems you will get from this completion will be gigantic, they will not have distilled the problem into a similar description of it's behavior, but instead created a more complicated way of observing that behavior. The Collatz-like problem I present here is a simplification of the behavior of this TM. If you observe the machine running you will see that it is effectively completing these transitions.
In other words, I am not arbitrarily choosing to convert this to a Collatz-like problem simply because it is possible. I am looking at the behavior of this machine and that behavior turns out to be Collatz-like naturally.
Of course none of this proves that my Collatz-like problem really is hard ... but as someone else here mentioned, being hard is not a mathematical thing, it is a belief we have about certain problems we cannot solve after considerable effort.
However, the Collatz-like problems you will get from this completion will be gigantic, they will not have distilled the problem into a similar description of it's behavior, but instead created a more complicated way of observing that behavior. The Collatz-like problem I present here is a simplification of the behavior of this TM. If you observe the machine running you will see that it is effectively completing these transitions.
In other words, I am not arbitrarily choosing to convert this to a Collatz-like problem simply because it is possible. I am looking at the behavior of this machine and that behavior turns out to be Collatz-like naturally.
Of course none of this proves that my Collatz-like problem really is hard ... but as someone else here mentioned, being hard is not a mathematical thing, it is a belief we have about certain problems we cannot solve after considerable effort.