Here are odds of winning combats, based on dice from troops (before spending cards). Attacker to the left, defender to the right. The chance of both sides rolling the same total, gives a slight statistical advantage to the defender in each case.
1:1 -> 41.67 vs. 58.33
1:2 -> 9.26 vs. 90.74
1:3 -> 1.16 vs. 98.84
1:4 -> 0.08 vs. 99.92
1:5 -> 0.01 vs. 99.99
2:1 -> 83.80 vs. 16.20
2:2 -> 44.37 vs. 55.63
2:3 -> 15.20 vs. 84.80
2:4 -> 3.59 vs. 96.41
2:5 -> 0.61 vs. 99.39
3:1 -> 97.30 vs. 2.70
3:2 -> 77.85 vs. 22.15
3:3 -> 45.36 vs. 54.64
3:4 -> 19.17 vs. 80.83
3:5 -> 6.07 vs. 93.93
4:1 -> 99.73 vs. 0.27
4:2 -> 93.92 vs. 6.08
4:3 -> 74.28 vs 25.72
4:4 -> 45.95 vs. 54.05
4:5 -> 22.04 vs. 77.96
5:1 -> 99.98 vs. 0.02
5:2 -> 98.79 vs. 1.21
5:3 -> 90.93 vs. 9.07
5:4 -> 71.81 vs. 28.19
5:5 -> 46.37 vs. 53.63