The idea behind limiting the cat-5 field size is not to throw people who've never raced before into a huge tight pack. If not after 10 races, when are people going to be ready for a big pack? I think the problems you mentioned will exist whether it's a 40 or a 100-person pack in a nontechnical crits. A hilly/windy road race will split the pack up and spit people out the back, as will a technical crit. The only large-field races I've done have had enough technical elements to spread things out enough that I've never experienced what you're talking about.