Part of the intention of using a swarm of Urbies was to deliberately let them fall behind the assault lance. They would use their full torso twisting to be able to always face the enemies while still being able to move forward. That way if the enemies got in front of them, but behind the assault lance, they would get shot with the autocannons. If the enemy get behind the urbies, they still get shot with autocannons. Obviously the torso twisting can't be a thing for the reasons aforementioned, but I completely forgot about the arms being able to face the rear. I think my plan may still have merit, sure the urbies can still get shot in the back but if the enemy is willing to spend the extra time to go behind the urbies to shoot them in the back then that is one less round that they are bothering the assaults. Maybe it is time to start perusing ebay for some urbanmechs. The only concern with using pure urbies as escorts is that the enemy is allowed to close range with my assault lance, to an extent. Then the question becomes, should I be concerned? As long as my units keep advancing, they can torso twist to shoot light units, so long as there are not better targets to shoot at, and the urbies can support them from the rear.
So what am I looking at for force composition? A forward lance to begin engagements and provide targeting for indirect fire (a mix of cavalry VTOLs, hovercraft, and fast mechs), an assault lance to bring the pain around midgame (specifically units with LRM-20 and -15 for indirect fire so they are always doing something), and a group of urbies to provide covering fire for the assault lance as they move forward. I like the sound of it personally. And it is more than feasible to run in the games I play point-wise, since we usually play 20,000 BV minimum. Maybe throw in a few firetrucks (literally) to put out fires for devious people like you MoneyLovingOgre4Hire.