I don't think giving speeds in any form is going to totally solve the problem: I think a lot of the problem is that a lot of the folks there have never done a race before, quite likely haven't trained, and have no idea what their speed will be. Then the times given in no way relate to a third of the field each.
So... we have inexperienced people with no idea of their time, but thinking they'll run all the way putting themselves in the first and second waves, because they assume that each wave represents a third of the field (and of course, many of them don't do as well as they thought...). Meanwhile because the times given in no way relate to the assumptions of the inexperienced, those who do know their time, and follow the rules, end up behind much slower competitors.
I think if there are going to be three timed waves, then their times should relate to the average times of a third of the field each. And they should be advertised in a way that gives more guidance to people who don't know their times. (Like I tried to do in my examples above)
If they are going to have a sub-25 wave then it should be advertised as only for experienced racers who have previously recorded times of that speed.
I also still think that restricting the width of the start could make a major difference... and having a 'slow lane' system rather than picking out walkers for silly and unrealistic restrictions.