Thanks for spoiling everything Jasper
But I knew that I'd missed something vital...
Light infantry are supposed to excel vs heavy infantry in 'difficult' terrain, such as mountains, swamps, (underwater?), forests, etc. They're also better at ambushes, hit and run tactics, skirmishing, night fighting, etc. While some units get a no-starve bonus in specific terrain (does anyone EVER take that into account when making strategic unit building decisions?), they don't get a fighting bonus, which is a damn shame as then you would be able to do some really interesting things like getting some lizzards to actually fight well (if only in swamps)...
Is there a place to suggest improvements to the appropriate people somewhere in this forum? Something like heavy inf. get a heavy encumberance penalty (+100%) when fighting in mountains, 50% in forests, etc. A 'attack and swarm enemy flank, then run away before the center has time to react' command might be interesting for fast LI.