One thing which always bothered me during my time in the 60th was how we were unable to skirmish effectively due to cavalry. Skirmishers should be doing quick flanking and daring maneuvers yet when there is cavalry you are forced to stay in close proximity to the lines. Merely having bayonets is a deterrant to cavalry because they know they can have much better results if they bide their time.
Most definitely if said cavalry are hussars, but heavy cavalry shouldn't have any more issues taking out a lone light inf line with bayonets. If there is competent cav running about, any attempts at splitting off from the main force will surely result in being diced and overwhelmed eventually. Line, light or rifles all the same.
Edit: What I'm trying to communicate is that the need for generalists just isn't there, if a force consisting of cav, lines and riflemen play in a reasonably organized fashion they will likely be more effective than a force being weaker due to having less line infantry. I have always looked at the line infantry as sort of an ankor for all other classes, skirms are a support unit, and if the line proves too ineffective there is simply nothing one can do to save the day in most situations, there are exceptions but they don't come by often.
Once or twice in almost every line battle there is a crucial melee, the outcome of this melee will likely determine the outcome of the line battle.
The roles of cav, skirms and arty are to try and sway the outcome before and during the engagement. Their effectiveness at doing this will "usually" decide the victor, varying competence of the lines non withstanding. What irks me about light infantry is that it simply isn't effective enough to warrant use in my opinion.
Their melee stats are shite, so helping the lines through melee simply wont do, and their shooting skills are again subpar in comparison to the riflemen, so why bother?
I'd take the extra line infantry every time.