Legs are the second toughest part of the mech, almost as tough as most mech's CTs. The problem is that jack-holes tend to strip the armor off of them for an extra ton or two of weapons and then cry when someone discovers they did it and exploits their foolish gamble.
Legs have approximately 2/3 - 5/6 of the internal structure damage capacity of the Center Torso. So a 20 ton mech's legs have 5 damage for the internals. Furthermore a mech can mount double the internal structure damage capacity in armor on a given location, this means that the same 20 ton mech can have 10 points of armor on the legs, for 15 damage capacity total. The center torso of a 20 tonner has only 6 internal points, with a maximum of 12 armor, but that also includes rear armor. Most light mechs only put 2 points on the rear torsos, meaning the CT has 10 armor and 6 internal, for 16 total. Killing a maximum armored 20 tonner is loads faster by blowing through the CT than the legs.
Similarly a 100 ton atlas has 47 armor on the front CT (14 on the rear), with 31 internal damage, for a total of 78 damage capacity. Each leg has 21 internal and ~42 armor, for a total of 63 damage capacity. Blowing off both legs would take a combined total of 126 damage, or almost double what it takes to carve through the CT.
The "Problem" with legs is that in CBT where these values were originally balanced, a leg was only hit 1:9 times, the least hit location next to the cockpit (which was 1:36). This meant that fully armored legs were rarely blown off (unless a shin kicking competition started, which it did often in 3025 games.)
In MW games the legs are extremely easy to hit because a.) they are big, b.) In MW:4 damage from one leg would transfer to the next leg, making it insanely easy to blow both off without even thinking about which one was a smoldering burning wreck.
Solve the problem of damage transfer by making hits on a "destroyed" leg do nothing, and increase leg armor and internals slightly based on their balanced values from CBT, and everything should feel about right.