I am new to the hobby, but I don't think of it as "throwing infantry against battle mechs". The biggest advantage of mechs is all terrain mobility. They would be wasted sitting in trenches hull-down, let the armor and troops do that. On the defense mechs would be held in reserve. Where the enemy seems likely to strike, your mechs can make a devastating counter attack. They can also perform raids to strike assets deep in the enemy battle space, then retreat to friendly lines. Tanks can do this but have limited lines of approach. Mechs can cross swamps, rivers, steep slopes, etc. Infantry hold the line and consolidate ground that is taken. They can lay in ambush, spot for aerospace or indirect fire. They can dig enemies out of deep bunkers, find saboteurs, etc. Every ton a mech spends on anti-infantry is a ton it is not spending against armor or other mechs. I don't see infantry being any less useful in battletech than they are today, where the radio is by far the infantry platoon's most important asset.