It's said about brain that, "use it or lose it" — now, question being, do you think if person plays brainless gambling games such as slots, dice for major part of his/her daily routine, will it make him/her dull?
Edit: "brainless" as in playing gambling games that does not require using brain, I thought it was clear especially given examples.
We have seen several gamblers try to make a strategy to outsmart this "brainless" game. From that the answer can be seen. The human mind keeps on working even if one doesn't see it. A working mind keeps developing, no matter how little it works, so to answer your question whether playing non-skilled games makes us dull is no.