if your summoner isn't at the league max, you could potentially get punished up to 7 times (once for the summoner and 6 more times for the reduced level splinters). Am I understanding this correctly?
No. From what I understand the card level gets counted even if it can't be played at that level. So if I have a level 1 summoner but play a maxed out rare card, I'd get full credit for the maxed out rare even though it plays at a lower level.