Localizer Approach and Timing to MAP Safety Concern

Unless you are equipped with fancy avionics, you're probably not able to determine the exact GS that you are descending at on a LOC approach. Assume two scenarios for a LOC approach with only a time-based MAP: you reach your calculated MAP earlier than the actual MAP or you reach your calculated MAP after the actual MAP. The first scenario seems dangerous since you will execute the missed prior to the runway threshold/actual MAP; the second, not as much as long as it's not a significant difference that will put you outside of obstacle clearance range. In the second scenario, tower can advise you that you flew past the runway threshold, but in the former, it may be too late for ATC to correct you. Obviously, the FAA established this estimating method knowing that it will be an approximation (right?), but is the consequence of a MAP miscalculation a valid safety concern? 

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