I believe the issue with game rules is not the time it takes to implement them, but the exponentially increasing amount of combinations possible. Putting game rules in will make people feel entitled to have the game work fully with all of them, meaning a lot of combinations have to be tested which increases testing time by a lot (especially if rules come from different versions of the code).
There's no need to test any other settings than the default ones. The designer can foresee what is the impact of the rules and I believe there was no complaints about the dozens available in vanilla. In fact and if anything, people want more rules to be coded, instead of complaining about those that exist.
In my large mod I never received a complaint about the rules I came up with ot their balance. Quite the contrary, my players receive said rules positively and request more rules to be defined.