This has probably been covered before but I thought I'd spell out an idea which I've had before (and if I posted it before please remind, I'm getting old). Say and InnerSphere military (led by some design strategist person) looks at the 20-ton-design and says these Mechs have limited military value. Screams Lyran right but objective they are pretty weak (internal structure and max armor value I'm looking at you) compared to 25-tonners which he, she or they would term the lightest of new Light BattleMechs. 20s would fall into a new Ultra-Light Category where they'd serve as auxiliaries (support roles, training, logistics, militia at first and then even out of there) at best, basically non-combatants.
Lights would now range from 25 to 40 tons (25, 30, 35, 40) and like all other categories there would be four integers of 5 ton design in each.
Medium would be 45 to 60 tons (45, 50, 55, 60).
Heavy would be 65 to 80 tons (65, 70, 75, 80).
Assaults would be 85 to 100 tons (85, 90, 95, 100).
Story wise this could have been an SLDF project that was never executed but thought of during the Golden Age. Perhaps the Arms Control Amendment of 2751 killed it as the Star League needed great numbers to project force and hence was dropped.
Thoughts??