I think it's simply a case where the amount of experience the hero should have gained from the battles didn't match up, and it's not even about the losses...
16 medusas - 480
24 dragonflies - 480
60 Gogs - 780
Let's assume the maximum number of champions, which is 19 - 1900
Total: 480+480+780+1900=3640, which is 5 levels. What's the inconsistency?
Oops, my mistake, 4 levels, but Shakti must have defeated something else during that time anyway)). But the hint is about a lack of experience, not an excess.