Maybe your fighters are busy elsewhere.
Anyway, are the odds of success the same if we multiple 10 fold?
Let’s see!
10 Inf + 10 Art has Attack Punch 40
10 Inf Defending has Defense Punch 20
In one round you have a 65% chance of hitting 7 defenders (9% chance to win in one round)
10 Inf + 10 Arm has Attack Punch 40
10 Inf Defending has Defense Punch 20
In one round you have a 68% chance of hitting 7 defenders (8% chance to win in one round)
In LL, regardless of Arm or Art, if you have 10 Inf + 10 Art (or Arm) you have Attack Punch 40
10 Inf Defending STILL has Defense Punch 20
In one round you have a 70% chance of hitting 7 defenders (0% to win in one round.)
As you can see, the microcosm holds true for the macro-scale. The results are still way off from ADS in LL, thus, LL is NOT a good indicator of good tactics to use in ADS. (And vice-versa.)
They are both fun games to play. They are NOT the same. The tactics are NOT the same. ADS battles and LL battles don’t need the same force compliments. LL only needs punch. ADS needs units of strong punch individually to increase odds of hits.
I’d be just as happy to send inf/art into battle in LL as I would inf/fig if I could use the figs somewhere else and the territory is secure from counter attack. (ie you are liberating Archangelsk and England had just liberated karelia preventing Germany from attacking Archangelsk.)