you are right, the full power of ls will be unleashed when your damage output is high, so especially in the higher levels in most cases.
i usually start using a ls charm at level 20-25 and use lpk/lpa gear before, this works very fine with my gear ( 70-100 ee weapons )
but having a ls with low level req doesnt exclude that you start using it later then when your damage is higher
its the only one i found, so there will certainly be better choices with higher rates.
its a math questions which gear you pick. imho pure damage is not everything.
lets say you hit for a constant 100 damage, 10 life steal will bring you 10 life back with every hit.
this can be very nice in long lasting battles.
personally, i was very sceptical on it at first as i would also loose quite a lot stat points, but when i tried the ls gear for the first time the result was really astonishing.
i switched my medium level charm from this:
Rare lightning VII
Level Req: 20
Spell Damage: 8 to 84
Mana Cost: 65
+33 Dexterity
+1% Physical Damage Reduction
to
Angelic wild heal VIII
Level Req: 25
Heals: 9 to 98
Mana Cost: 75
+12 Intelligence
+2 Critical Strike
+8% Life Steal
+3% Critical Flux
and also use this armor now:
Angelic sapphire chain mail
Level Req: 30
Defense: 27 to 69
+8% Experience Gained
+7 Extra Item Slots
+1 to 20 Mana per Kill
+7% Life Steal
the fights last longer basically then if i would use the stat gear, but i can do much more fights in a row and even recover to full life through the battles.
I do remember that trial testing you did a few pages back on it. Currently, my HC barb uses a 6% LS charm and I do notice the difference. My dmg is really low, though I do steal enough life where I'm able to chain more mobs than normal. I guess it wouldn't hurt to try LS gear even at lower levels and see which may be better. My armor and charms don't have high stats on them anyways =X