Here are the chances of drawing at least 5 events in your 13 initial cards for the ability, depending on the number of events in your deck. This includes Painted World in the total of 36 starting cards (weaknesses are reshuffled). Also included are chances if 2 cards are added during the campaign for comparison. This is calculated using a hypergeometric distribution (appropriately assuming no replacement):
Number of Events: Chance of drawing at least 5 in 13 -> New chance of at least 5 in 13 if 2 non-event cards are added
24: 99.9% -> 99.6%
23: 99.7% -> 99.1%
22: 99.3% -> 98.2%
21: 98.5% -> 96.8%
20: 97.2% -> 94.6%
19: 95.0% -> 91.5%
18: 91.8% -> 87.2%
17: 87.3% -> 81.7%
16: 81.3% -> 74.8%
15: 73.9% -> 66.8%
14: 65.0% -> 57.7%
Hopefully this will help with some of your optimization.