try this on for size:
Raid Shadow Legends Champion Leveling Guide | AyumiLove
4 STAR CHAMPION (MAX LEVEL 40)
Total XP Required: 449,082 | Rank Up Silver Cost: 22,400
Normal Stage 12-6 XP: 1,834 per champion (245 Rounds x 4 Energy = 980 Energy)
Hard Stage 12-6 XP: 2,950 per champion (153 Rounds x 6 Energy = 918 Energy)
Brutal Stage 12-6 XP: 4,400 per champion (103 Rounds x 8 Energy = 824 Energy)
Nightmare Stage 12-3 XP: 9,604 per champion (47 Rounds x 16 Energy = 752 Energy)
3 STAR CHAMPION (MAX LEVEL 30)
Total XP Required: 200,681 | Rank Up Silver Cost: 9,600
Normal Stage 12-6 XP: 1,834 per champion (110 Rounds x 4 Energy = 440 Energy)
Hard Stage 12-6 XP: 2,950 per champion (69 Rounds x 6 Energy = 414 Energy)
Brutal Stage 12-6 XP: 4,400 per champion (46 Rounds x 8 Energy = 368 Energy)
Nightmare Stage 12-3 XP: 9,604 per champion (21 Rounds x 16 Energy = 336 Energy) 3 STAR CHAMPION (MAX LEVEL 30)
So, for those number of rounds, and look at your time for a round and see if it makes sense.